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Wire Guage Table For Spa Wiring


Chip C.

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Where can a guy find a table that shows the wire size AWG required for wiring up a hot tub? It would show wire guage corresponding to amps load, and maybe include the length of the run too.

I'm sure somebody here knows where to lookup this info on the Net, or can post a table. Probably useful to lots of people on this forum.

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Contact an electrician. Wire size is more complicated than some chart. The conditions the wire is subject to, the insulation used and the type of conductor all are part of the equation.

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Contact an electrician. Wire size is more complicated than some chart. The conditions the wire is subject to, the insulation used and the type of conductor all are part of the equation.

Jim,

With all due respect, I really don't need a guru that has no information to offer up, to tell me to "call an electrician." I am a committed do-it-yourselfer, and if I wanted to hire this work out professionally, I would have obviously already done so. That is why I posted this on a spa help forum instead of picking up the Yellow Pages. I'm a skilled carpenter and tradesman, and I think I can handle the electrical work as I've done quite a bit of wiring on my own home that has passed inspection. As a matter of fact, a neighbor two houses down just had his spa wired up by an electrician, and guess what? You guessed it, he miswired the GFCI and then tried to blame the spa store for defective product when it was his fault (pun intended) all along. So I think I will do the wiring myself. It's not rocket science, and not dangerous if you have a brain and follow the rules-- just like anything else.

Having said that, I did look at Dr. Spa's table and it really does not tell me what I need to know about wire gauge. The Sundance manual says use #6 wire for 50A, but says nothing about the length of the circuit, and my spa is over 15 ft. away from the subpanel with a half-circuit length of maybe 150 ft. total to the service. Dr. Spa's table says #8 THHN wire (run in PVC raceway by the way) is good for 55A, but that can't be right. There is a wire resistance calculator, but does not indicate what the rule is for voltage drop and going up to the next larger size wire, etc. So that is not much help either.

By the way, this has nothing to do with my question, and I mean no offense. But the name looked familiar with something I read a few weeks back, so I Googled "James Arjuna" and you would not believe what I found. Check out "James Arjuna" for yourselves by using the Google box at the top of this page. Truly amazing stories.

Any help from a pro or experienced do-it-yourselfer would be appreciated!

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Contact an electrician. Wire size is more complicated than some chart. The conditions the wire is subject to, the insulation used and the type of conductor all are part of the equation.

Jim,

With all due respect, I really don't need a guru that has no information to offer up, to tell me to "call an electrician." I am a committed do-it-yourselfer, and if I wanted to hire this work out professionally, I would have obviously already done so. That is why I posted this on a spa help forum instead of picking up the Yellow Pages. I'm a skilled carpenter and tradesman, and I think I can handle the electrical work as I've done quite a bit of wiring on my own home that has passed inspection. As a matter of fact, a neighbor two houses down just had his spa wired up by an electrician, and guess what? You guessed it, he miswired the GFCI and then tried to blame the spa store for defective product when it was his fault (pun intended) all along. So I think I will do the wiring myself. It's not rocket science, and not dangerous if you have a brain and follow the rules-- just like anything else.

Having said that, I did look at Dr. Spa's table and it really does not tell me what I need to know about wire gauge. The Sundance manual says use #6 wire for 50A, but says nothing about the length of the circuit, and my spa is over 15 ft. away from the subpanel with a half-circuit length of maybe 150 ft. total to the service. Dr. Spa's table says #8 THHN wire (run in PVC raceway by the way) is good for 55A, but that can't be right. There is a wire resistance calculator, but does not indicate what the rule is for voltage drop and going up to the next larger size wire, etc. So that is not much help either.

By the way, this has nothing to do with my question, and I mean no offense. But the name looked familiar with something I read a few weeks back, so I Googled "James Arjuna" and you would not believe what I found. Check out "James Arjuna" for yourselves by using the Google box at the top of this page. Truly amazing stories.

Any help from a pro or experienced do-it-yourselfer would be appreciated!

WOW.

Chip, I think you need to remember that you asked the question. The answers are free. (even if you don't like them.) No need to attack the people trying to help.

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Hey, I do appreciate the answers. Not one word of attack in my post intended. The other day the next door neighbor lady asked me if I knew how to unplug a toilet. I showed her how to use a plunger to unlodge the hunk of poop-- I don't think she would have appreciated it much if I just said "call Roto Rooter". That was my only point... The wife's always telling me I'd be better off if I kept my pie-hole shut, so sorry if I offended anybody.

Is there anybody out there in poolspa forum-land that knows the basic rules-of-thumb for spa wiring?

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I wired up my own tub. I had 6-3 already pulled to a box under the house for the stove. We use gas now so I was able to run it to the tub. Made it real simple.

I looked into the Amps vs wire thing. I know that 6-3 wire is rated for 55 amps, but it can be protected with a 60 amp circuit. So that is what I did. Ran 6-3 wire coming from a 60 amp breaker. The run for my tub is only maybe 30 ft total. 18ft from main panel to the sub and then 12ft more to the spa.

If it makes you feel any better I ran 6-3 to my detached garage from a 60 amp circuit 2 years ago. It was a run of about 90 ft and I haven't had any problem with it. When I had electricians to the house to wire my kitchen remodel (pros are faster and I didn't want to mess with multiple 3-way switches) I asked them about it and they thought it was perfectly fine.

So there you have it. Definitive information from some guy on the net. ;)

Hey, I do appreciate the answers. Not one word of attack in my post intended. The other day the next door neighbor lady asked me if I knew how to unplug a toilet. I showed her how to use a plunger to unlodge the hunk of poop-- I don't think she would have appreciated it much if I just said "call Roto Rooter". That was my only point... The wife's always telling me I'd be better off if I kept my pie-hole shut, so sorry if I offended anybody.

Is there anybody out there in poolspa forum-land that knows the basic rules-of-thumb for spa wiring?

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Jim is right, however if you want to do it yourself at least have it inspected and tested by a qualified electrician. There are quite a few factors that have to be taken into account in cable selection.

Also I suspect that 'electrician' who wired the spa incorrectly was not a proper electrician. I know of people who claim to be certain tradesman and they have not been anywher near a college or had any formal training whatsever.

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I am a committed do-it-yourselfer, and if I wanted to hire this work out professionally, I would have obviously already done so.

I'm with you, Chip. Many people manage to make it through life without hiring experts for everything, and home wiring isn't rocket science. My apologies to journeyman electricians out there, but you know it's true. I operate a subatomic particle accelerator for a living and I can tell you that it's not rocket science, either. Like home wiring, anyone can do it if he/she is of average intelligence and has the interest in learning why things are done a certain way.

As to spa wiring being "complicated" (as one responder stated), I respectfully disagree. It's actually pretty straightforward, and wire type and insulation type is basically constrained by what you can buy at Home Depot or Lowe's or whatever. You'll find that they all carry pretty much the same thing, and it meets or exceeds the NEC requirements for everything you'd do at a residential installation. Chances are, if you hired a local electrician, he or she would use exactly the same thing you're going to buy.

Spa manufacturers typically suggest using #6 wire without mentioning distance probably because most home spa installations involve wire runs of no more than several tens of feet, which will not result in unacceptable voltage drop. The primary concern with wire size is ampacity. If you use 50A service for your spa and you have a continuous run, #6 will be fine in that regard. If you can go up a size to #4 you will see slightly higher voltage at the spa, especially if the run is particularly long. However, pulling wire gets to be substantially more difficult as the size goes up.

I don't have the NEC tables in front of me but I did when I wired my spa two years ago and I chose #6. The large wire at Home Depot is dual-rated THHN/THHW, which is exactly what you want anyway. If you use "Romex" (sheathed conductors), you will probably need to go up a size because sheathed wires must be de-rated compared to individual conductors.

One recommendation I can make from experience is to always use the absolute largest conduit that you can reasonably accomodate. The difference between a totally simple, almost fun installation and a dirty, sweaty, frustrating, knuckle-busting installation is in the wire pull. Larger conduit not only makes it a snap, you will also be using larger pull boxes -- and that's where the REAL difference lies. Fill tables in the NEC are not about conductor temps or anything like that; they're all about being able to pull the wires. Unless you have reason to use conduit sized to the fill tables, ALWAYS go larger! I used 1-1/4" (which is oversize) but would have been happier using 1-1/2". My mantra now: CONDUIT IS CHEAP. The cost of PVC conduit is trivial, and although the pull boxes cost more in larger sizes, it's still in the noise compared to the whole project (and you probably only need a few anyway). You can always use adapters to size large stuff down to match existing panel openings if necessary.

Good luck, and report back when your spa hookup is done! I suspect you won't have any insurmountable obstacles.

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Craig,

I enjoyed reading your eloquent and thoughtful comments. I will choose oversize PVC conduit for certain, and report back when my project is completed. I do wish I knew the rule-of-thumb, as it relates to voltage drop % and moving up to the next higher AWG guage, but will wing it using #6 THHN CU stranded conductors.

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I do wish I knew the rule-of-thumb, as it relates to voltage drop % and moving up to the next higher AWG guage, but will wing it using #6 THHN CU stranded conductors.

You can use an online calculator if you're really concerned. The one at http://www.powerstream.com/Wire_Size.htm says a 50-foot run (100 feet round trip) of #6 copper wire at 240V, loaded to breaker capacity (50 amps) drops about 2 volts. It won't be a problem.

Craig

Sunnyvale, California

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Chip, I just re-read the post where you mentioned the wire run and realized I mistakenly read "50 feet" rather than 150. If that's truly the one-way run you'll be putting in, the drop with #6 is actually about 6 volts at breaker capacity -- although you won't ever actually draw that much current in use, because of course it would trip the breaker. If you're worried about it and you can fit #4, that size drops 3.8V at full breaker current.

But is your one-way run really that far? Maybe I'm just used to the small suburban lots around here; at my house, you'd need to run a wire diagonally all the way from the very front corner of the lot to the opposite back corner to get 150 feet!

Craig

Sunnyvale, California

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Craig,

You astutely caught my mistake. I mis-stated my run as 150 ft. "half-circuit" when actually it is 150 ft. circuit, or just a 75 ft. one-way run. I WISH my lot was that big! I know you know, so at what drop in voltage do you like to upsize? I know my actual load will rarely approach the circuit capacity, but knawing intellectual curiosity has always been my downfall, or so my wife tells me.

Chip

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I'm more than willing to give advice but to rebutt the idea that most homeowners should do there own electrical I'll give my 2 cents. Almost every homeowner wiring job I've seen is wrong, it's unsafe and not up to code or any reasonable standard. That aside I believe there are a few non-electrical professionals capable of safe work. I'm sure whomever did all the substandard work I've seen thought it was just fine.

If your spa gives you the size of wire that you are supposed to use then use it. For the most part they either match the NEC or over wire it. If the manufacture specs exceed the NEC you are required to meet them. You mentioned 15' to a sub panel. If that is the case you do not have to account for voltage drop. Even at 150' I wouldn't worry about it myself. If you are looking for ampacity tables in the NEC see 310.16. And you need to understand that you looking at that #8 and thinking it is good for 55 amps is assuming that your terminals of of your hot tub and disconect are rated at 90 degrees. You need to match that temp column to the lowest rated terminals you are connecting to and if you don't know the rating you need to use the 60 degree column. Or just use the manufactures specs. I'm off to bed. Feel free to post any specific questions.

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...at what drop in voltage do you like to upsize? I know my actual load will rarely approach the circuit capacity, but knawing intellectual curiosity has always been my downfall, or so my wife tells me.

Well, my installation probably isn't much longer of a run than yours will be, and I happily went with #6. For me, the breakpoint involves balancing the cost, the potential for problems, and the tolerance of the load. THHN/THHW in a big conduit doesn't present a heat issue, and spa pumps aren't likely to have a problem with a 2% reduction in supply voltage. The cost difference between #6 and #4 is not insignificant, plus #4 is much harder to pull. These issues were in my mind when I did my installation, and I decided to use #6.

I pay a lot more attention to voltage drop in low-voltage high-current circuits, such as in boats and RVs. Rule of thumb for me is in the 2% region, but again it's an ad hoc deal. Cost is also a consideration. If being slightly more conservative costs only a tad more, I often go for it. But if it's a lot more expensive -- as well as a much bigger hassle -- to go with bigger wire in a situation that doesn't seem to justify it, I'm OK with smaller/cheaper.

I'm sure you'll be fine, Chip. Get that spa hooked up and enjoy the soak!

Oh, and if intellectual curiosity is problematic, I'm doomed. :)

Craig

Sunnyvale, California

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Almost every homeowner wiring job I've seen is wrong, it's unsafe and not up to code or any reasonable standard.

The code is the size of a Manhattan telephone book. It's pretty much guaranteed that someone can find fault with SOMETHING that was done by a layperson, but that doesn't necessarily mean it's unsafe or problematic.

I maintain that wiring a home spa is something that can be done safely even by people who don't get paid to do it. But then again, I'm clearly an outlaw. I also <gasp!> work on my own car! :)

Craig

Sunnyvale, California

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I'm more than willing to give advice but to rebutt the idea that most homeowners should do there own electrical

Any literate person of average intelligence, with the ability to use a screw driver, pliars, snips and wire strippers, is capable of doing their own wiring. There are plenty of good resource books available at any home center (or library) that show the right way to do all types of home electrical wiring, and of course a wealth of information on DIY websites for those in need of more information. As in all things, the only prerequisite is the desire to better oneself by leaning how to do things correctly. There is no mystery to it, nothing to fear, no trade secrets. Such work yields the potential for the great satisfation of saying "I did it myselft, and I did it right." There are only one or two things I can think of that feel better than that!

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I'm sure that you're capable of it but some people have never wired anything let alone a hot tub. And when I say that all the homeowner wiring I've seen is subpar I mean that I wouldn't consider it safe. Not that it is mildly deficient in a few code references but just plain out unsafe.

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...when I say that all the homeowner wiring I've seen is subpar I mean that I wouldn't consider it safe. Not that it is mildly deficient in a few code references but just plain out unsafe.

Would you please post the specifics about these clearly unsafe wiring situations? It's possible that I (and others) might make some of the same mistakes without realizing it. I for one am always interested in learning. Thanks!

Craig

Sunnyvale, California

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I say that all the homeowner wiring I've seen is subpar I mean that I wouldn't consider it safe. Not that it is mildly deficient in a few code references but just plain out unsafe.

I have no doubt that what you have observed is true, but think about it for a moment. I could honestly say that all of the prisoners I have ever seen are convicts. Also true, but most people are neither prisoners nor criminals. So, when you see sub-par wiring, it is a fairly safe assumption that it was not professionally done. But I doubt when you've seen good wiring, you interrogate the homeowner or past owners of the property to find out if the work was done by a licensed electrician or just a job well done by a regular Joe.

If you were to inspect the electrical work I have done on my own property, the only difference between my work and a pro is that since I am such a neatness fanatic, everything has to be perfectly straight and organized, even in the service panel. I go way too far, and would never make any money as a pro electrician because I spend way too much time on it making it not only function properly, but look pretty. But I don't pay myself much, so I can get away with spending a lot of time on it.

On the other hand, I work with all kinds of professional tradesmen on a daily basis, and am sorry to report that I see sub-par work from time to time even amongst those well-paid for their work. On a job we finished last week, the insulation contractor had to leave early before finishing up on one of the outside walls. The sheetrock crew arrived, and installed drywall over the uninsulated wall. The homeowner will never know about it, although over the lifetime of the home, it will cost them thousands in wasted heating. The worst part, when the insulation guy came back the next day, he was overjoyed that he did not have to finish. I could go on and on with most all of the different trade disciplines, but am straying already too far off topic and dinner is getting cold.

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Craig,

I don't want to dwell on do it your selfers vs the "pros" I agree with chip that some work by the supposed pro's is shoddy. You need to interview your prospective contractors and try to get good refrences. The lowest bidder/price is not usually the best. As far as things I've seen they range from 4 wire dryer plugs being fed with a 3 wire. To large a breaker for a conductor. Ground used as a neutral. In wall splices. Loose connections. Lots of stuff. Feel free to ask any questions you have. There are a few other electricians poking round this site to : )

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As far as things I've seen they range from 4 wire dryer plugs being fed with a 3 wire. To large a breaker for a conductor. Ground used as a neutral. In wall splices. Loose connections.

I'd say the people who made those mistakes didn't understand why things are done a certain way and made no attempt to learn before doing the work. If the above stuff is what you always see then I suppose it's understandable that you assume the worst, but I assure you that many normal homeowners are capable of doing safe electrical wiring. You just don't see their work because you have no reason to -- and crappy work is naturally what gets noticed.

Craig

Sunnyvale, California

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If you were to inspect the electrical work I have done on my own property, the only difference between my work and a pro is that since I am such a neatness fanatic, everything has to be perfectly straight and organized, even in the service panel. I go way too far, and would never make any money as a pro electrician because I spend way too much time on it making it not only function properly, but look pretty. But I don't pay myself much, so I can get away with spending a lot of time on it.

This in a number of cases is very true, some electricians, like some other trades, just want to get in and get the job done. We always work on the assumption that a tidy and neat job is a job well done.

Anyway back to the original post, cable selection is made by taking various correction factors into account and external influences. If you do the install yourself then I still suggest that it is tested and inspected. You need to make sure, as well as other things, that the protective device and RCD trip out within the specified times.

When tested, inspected and you are given a certificate this will give you peace of mind that the installation is safe.

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I will keep that in mind, but there really are not a lot of corrections or

external factors to take into consideration in a circuit as simple as a portable

spa hookup. Since I am using approved THHN #6 CU, in an oversized raceway, the

only external consideration is the length of my circuit, which is not excessive

from what I have heard.

Because of the reactive loads that spa circuits present and the fact that my

ozonator runs on a 120V leg, I have decided to use a standard 50A double-pole

breaker in my house service panel rather than a GFCI breaker, and use an

inductive GFCI device (what you call an RCD in merry old England) with separate

high-current contactor as the disconnect panel. This should reduce or eliminate

the errant false tripping that is so common with spa owners that I have

conversed with. (I first read about this type of subpanel on Jim Arguna's

website by the way, and I agree 100% with him-- it's the way to go, an elegant

solution to a nagging problem).

There are a couple of these types of disconnect panels on the market; I found one made by Connecticut Electric

for about a hundred clams that is big enough for my spa (50A) and looks like it

will be just the ticket. It also has an integrated 110 volt breakered branch

circuit that I don't really need, but if I ever want to add another outdoor

outlet for the Weed-Whacker, its there.

Yes, I will get the required inspection and have already bought my permit so the

county got their blood money.

There is one extreme danger in homeowner wiring:

I have assured my wife that the life

insurance premium has been paid, in case I get mugged for the copper wire on the

way back from Lowes.

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