#6 Ground Wire? Spa wiring requirements

[5030tinkerer]

My house is pre-wired for a spa. Trouble is, that the wiring is 6/3 and behind sheetrock (of course it is). With 6/3 comes 6 gauge hot in red, 6 gauge hot in black, a 6 gauge neutral, and a bare 10 gauge ground. The installation directions (http://www.olympicho...manual_2013.pdf) for the spa indicate #6 wire for all four of these wires for wire distances of up to 100'.

I measured my wire length from my main electrical service panel to where the spa panel would be and came in at 34 feet. From http://www.calculato...es=50&x=64&y=13, it would seem that the electrical carrying ability of #10 wire is greater at this distance than #6 wire has at 100 feet since the voltage drop is half a point less with the 50 amp load I popped in there.

Am I stuck ripping open my wall or would this be a safe install as is?

Adding confusion is the following verbiage from p 14 of the install manual (when the diagram on the following page calls for #6): 'An electrical subpanel containing two GFcI breakers is included with each spa. We recommend that this subpanel be used to supply power and protect the spa. This subpanel requires a 70 amp, single phase, 230 volt, four wire service (two line, one neutral, one ground). The ground wire must never be less
than #10 AWG. use Nec 250-122 (table) and local codes for more information. A minimum #6 AWG solid copper bond wire is also required.'

The NEC table can be found at http://www.safecoelectric.com/images/resources_pdf/NEC2008 Table 250.122.pdf and indicates that #10 wire is good for up to 60 amp service (but again this is designed for 100' wire lengths).

 

[Western]

iirc, 10g is rated up to 30a . 8g 40a and 6 for 50a

 

[5030tinkerer]

You are correct, but these ratings are generally based on a 3% maximum voltage drop at a given amperage for a 100' distance. If you have a 1' long section of 10 gauge wire, for example, that wire can pull 1650 amps at a 3% voltage drop. Crazy, heh?

The open question is whether there is something 'special' in a grounding application and, especially, in a grounding application with a spa.

 

[Western]

Yeah I wouldn't know that, but would assume since it is a appliance with water and people, all precautions would be prudent. Personally I would follow the install to a "T"

 

[s219]

It's common for the ground wire to be a size or two lower. If I recall code correctly, ground does *not* need to be sized for the current carrying loads of the hots and neutral. So the distance/drop calculations aren't exactly relevant.

Also, the max current ratings of wire have nothing to do with voltage drop or length. It's all about temperature and capacity. You cannot alter the rating of a wire just because it's short. No way you will ever see a 1650A rating for 1 foot of #10 just because it's only 1 foot.

The normal procedure is to choose gauge based on the current load. Then upsize as needed to offset voltage drop. As an example, my barn branch circuit (for a 120V receptacle and lights) is 15A, which otherwise needs #14 copper to handle the max current. However, due to the distance, I upgraded to #6 (AL) so the voltage drop would not be a problem. We needed to be able to run power tools during construction.

Same for my pier circuit to a boat lift. It only pulls 12A, but we ran #10 copper because of the distance.

 

[5030tinkerer]

It's common for the ground wire to be a size or two lower. If I recall code correctly, ground does *not* need to be sized for the current carrying loads of the hots and neutral. So the distance/drop calculations aren't exactly relevant.

Also, the max current ratings of wire have nothing to do with voltage drop or length. It's all about temperature and capacity. You cannot alter the rating of a wire just because it's short. No way you will ever see a 1650A rating for 1 foot of #10 just because it's only 1 foot.

The normal procedure is to choose gauge based on the current load. Then upsize as needed to offset voltage drop. As an example, my barn branch circuit (for a 120V receptacle and lights) is 15A, which otherwise needs #14 copper to handle the max current. However, due to the distance, I upgraded to #6 (AL) so the voltage drop would not be a problem. We needed to be able to run power tools during construction.

Same for my pier circuit to a boat lift. It only pulls 12A, but we ran #10 copper because of the distance.

No doubt that the normal procedure is to choose gauge based on load, based on the Code. What's interesting is that if you pop even a 900 amp load into the calculator at Wire Size Calculator, you'll see that it specifies a 12 gauge wire. From this, it would seem that the electrical carrying ability of wire (ampacity) IS indeed based on distance, but that National Electric Code doesn't want people choosing wire size on distance when the run is less than 100', but on their resultant thoughts on allowable voltage drop. That same calculator, when presented with a 50 amp load, specifies a #10 wire for wire lengths up to 28 feet, but doesn't specify a #6 wire until the 47-73 volt range. Sadly, as my wire length is going to be closer to 34', I'm in the 8 gauge range (smaller wire than I have now).

I might as well rip the wall and ceiling open and put in the #6 wire that they specified UNLESS someone can tell me why it is that it is normal for the ground wire to be allowed smaller.

 

[Inspector507]

The ground wire does not need to be full sized based on the load. Load current and voltage drop have little to do with it. The grounding conductor is there to create an effective ground-fault current path back to it's supply source to facilitate opening of the circuit breaker in a fault condition. Short circuit current and and load current are different.

 

[5030tinkerer]

The ground wire does not need to be full sized based on the load. Load current and voltage drop have little to do with it. The grounding conductor is there to create an effective ground-fault current path back to it's supply source to facilitate opening of the circuit breaker in a fault condition. Short circuit current and and load current are different.

Are you saying that the #10 grounding wire is fine in this application, then, and I *DO NOT* need to rip open my wall and ceiling to gain the access?

 

[teejk]

Are you saying that the #10 grounding wire is fine in this application, then, and I *DO NOT* need to rip open my wall and ceiling to gain the access?

Back up a bit...the instructions said the "bonding wire" needed to be #6, everything else minimum #10. We need a few "sparkies" to explain "grounding" vs. "bonding". It's confusing to me especially with that "single point grounding" change but I think it describes the wire from your main panel to its grounding source.

 

[5030tinkerer]

The wiring diagram on page 15 (attached in line here) contemplates the run from the main panel to the spa panel as needing to be #6 wire, but then discusses a #10 as a requirement elsewhere (where the 'converted' install isn't performed).

 

[teejk]

The wiring diagram on page 15 (attached in line here) contemplates the run from the main panel to the spa panel as needing to be #6 wire, but then discusses a #10 as a requirement elsewhere (where the 'converted' install isn't performed).

I'm not a sparkie but the wiring diagram seems to be pretty clear. I guess it makes sense because they have you feeding a supplied sub-panel and the GFCI's don't come into play until then. I was thinking you could install the subpanel closer to your main panel and using the existing wires run to the spa (just a little jump from the main to the sub and the GFCI's would take over from there) but the diagram seems to say #6 all the way to the control box. I think it is overkill (might be their legal department) but if you ever want to sell the house, it's a "pay me now or pay me later" thing. Time to call a sparkie I think. They are pretty good at fishing wire with minimal damage.

 

[Inspector507]

The #10 should be fine

 

[teejk]

The #10 should be fine

You think? This grounding/bonding/single point grounding stuff has a lot of us scratching our heads (including the pros). E.g. if you install Dish or Direct TV or Hughesnet or anything like it, code says everything has to come back to the same grounding source as your main service. No separate ground rods but a lot of wire and what they call a grounding block attached to the outside of the house connected to the main ground (funny in that I don't think that block could handle #6).

 

[s219]

No doubt that the normal procedure is to choose gauge based on load, based on the Code. What's interesting is that if you pop even a 900 amp load into the calculator at Wire Size Calculator, you'll see that it specifies a 12 gauge wire. From this, it would seem that the electrical carrying ability of wire (ampacity) IS indeed based on distance, but that National Electric Code doesn't want people choosing wire size on distance when the run is less than 100', but on their resultant thoughts on allowable voltage drop. That same calculator, when presented with a 50 amp load, specifies a #10 wire for wire lengths up to 28 feet, but doesn't specify a #6 wire until the 47-73 volt range. Sadly, as my wire length is going to be closer to 34', I'm in the 8 gauge range (smaller wire than I have now).

I think you are grossly missing the point -- that is a voltage drop calculator, and only a voltage drop calculator. And not a very elegant one. The better ones will also factor in wire load and ampacity, and will not specify a wire that is too small for a load, even if the voltage drop is acceptable. Note the fine print on that site:

"This Calculator will determine the minimum size conductor needed based on a 3% Voltage Drop. It does not take into consideration other factors such as minimum ampacity based on the National Electrical Code Table 310-16. (Allowable ampacities of conductors). Consult The NEC for further details."

So please understand that voltage drop has *nothing* to do with allowable ampacity. And ampacity has nothing to do with distance. It doesn't matter if your #12 wire is 1 inch long or 1000 feet long -- it's going to melt if you tried to pass 900 amps.

 

[grsthegreat]

the wire is fine. all 10/3 romex comes with the derated ground wire. dont let this bother you. there are literally millions of spas running it that way.

 

[grsthegreat]

also note. a 200 amp house panel will only have a #6 bare ground wire and 4/0 alum (2/0 copper) main feeds

 

[CobyRupert]

Grounding and bonding is the hardest to understand.
To be by NEC code, the table you originally listed is the correct reference. A #10 is good for up to a 60amp circuit (that is, a circuit protected by a 60 amp breaker). Next bigger size ground wire would be a #8, which can be used for a ground on up to a 100amp circuit.
I don't understand why the instructions showed a #6. I'm thinking a copy and paste typo error.
In all practically (i.e. regardless of where The Code draws the line) a #10 will be fine, especially is your subpanel has GFCI's.

Grounds do a couple things:
1) They (attempt to) equalize all potentials (voltage) on conductive services (enclosures, frames, etc.) and bond them to ground (0 Volts), reducing shock risk.
2)They provide a low resistance path back to the neutral of the transformer (not the earth!) when there is a short circuit to "ground". The low resistance allows (Ohm's Law) a large enough short circuit to flow so that the circuit breaker trips. Where the size comes into play is for this second purpose. If wire size is too small, the resistance may limit the current so that the breaker doesn't trip (as quickly). This is not a worry if you have a #10 versus a # 6, on that 60 or 70 amp circuit. The breaker will still trip on a fault.
The other issue with a small ground, is during those milliseconds before the breaker pops during a short circuit, by Ohm's Law again, a current on a larger resistance, this will cause a higher voltage rise across it, thus all the metal enclosures that use that ground will not be a 0 volts (earth) anymore and are at a greater shock risk during those milliseconds. But even a large ground wire only reduces this and doesn't eliminate it.
Also, because a greater resistance from a smaller cable lowers the short circuit current, the breaker might need a few more milliseconds before it trips, and a lot more energy has been let thru.

Bottom line: A #10 gnd, which is to code for a 60 amp circuit, will be fine for your 70 amp circuit.

 

[SPIKER]

From memory you said your LOCAL CODE requires a #6, if you ever plan to sell the place OR if something happens at the SPA and you did NOT wire it to LOCAL (and Fed Codes) then your insurance or sales may not pass/go thru...

That said the wire in the wall is NORMAL & could be used under normal conditions.

Bonding and Grounding are two different subjects, Bonding refers to tying the Neutral to the Ground or bonding the frames of equipment to the ground system/systems. Also note that if you are running a separate Sub Panel then that panel's Neutral must not be Bonded to the Ground Bus in that panel (from last ver of NEC not sure if that remained or not as I have not updated my NEC books as I'm out of the buis.)

Mark

 

[5030tinkerer]

From memory you said your LOCAL CODE requires a #6, if you ever plan to sell the place OR if something happens at the SPA and you did NOT wire it to LOCAL (and Fed Codes) then your insurance or sales may not pass/go thru...

That said the wire in the wall is NORMAL & could be used under normal conditions.

Bonding and Grounding are two different subjects, Bonding refers to tying the Neutral to the Ground or bonding the frames of equipment to the ground system/systems. Also note that if you are running a separate Sub Panel then that panel's Neutral must not be Bonded to the Ground Bus in that panel (from last ver of NEC not sure if that remained or not as I have not updated my NEC books as I'm out of the buis.)

Mark

Hey Mark! I don't recall mentioning my local code. If I did, I sure didn't mean to. Where I'm at, whether right or wrong, there is no code, no inspectors, no permits to pull, nothing. I just want to do the right and safe thing and don't understand the basis for the #6 wire requirement. I really and truly don't want to have to open my wall (and attempt to match the texture again!) if there isn't benefit, but want to be safe as well. We all know that safety and 'code' don't necessarily go hand in hand (in other words, you can be perfectly safe and not 'to code', but I am also mindful of the fact that the code is there for a reason that extends far beyond bureaucracy - it's *primarily* (or at least mostly) to keep the current people safe from themselves and future people safe from the poor implementations of earlier folk. I completely respect that.

My house is built well beyond 'code' in so many respects, but I hate going back and re-doing stuff at the same time, especially if it doesn't need to be.

In this application, the 70 amp spa panel is fed from a 200 amp main panel that is in turn fed by a meter panel with a 200 amp breaker. A grounding rod is connected to the main panel, but I don't recall the wire size connected to it - it's something like a multi-strand cable with maybe 5-7 #10 wires IIRC.

Regardless, what a great discussion! I haven't been able to be on this board near as much I used to be, but know that I can always count on TBN when I need it. What an amazing set of people on here! Thank you!

Inspector507 - do I remember that you are in electrical inspector by trade?

s219 - You said that wire length has nothing to do with 'allowable' ampacity. Do I correctly understand that then that a #14 wire, for example, that is rated for 15 amps of current, but happens to be at, say, 20' in length, simply cannot handle a, say, 30 amp draw - that it'll turn into a fuse, or minimally run hot and be a fire hazard?

CobyRupert - You say that #10 is good for up to a 60 amp circuit. In this case, a singular ground wire is handling a 70 amp PANEL, but one with a 30 amp GFCI, a 20 amp GFCI, and a second 20 amp GFCI breaker. It would seem logical, that any fault would impact only one of these breakers at a time, meaning that the #10 is actually MORE THAN plenty - for the same reason that the #4 wire evidently commonly used as ground in a 200 amp panel,is sufficient (surmising that this basis has to do with the max supported breaker size of 100 amps in that panel).

CobyRupert#2 - Thanks a ton for the grounding explanation. You said that 'low resistance allows (Ohm's Law) a large enough short circuit to flow so that the circuit breaker trips'. Doesn't resistance also increase with wire length? IOW, if the instruction manual calls out #6 wire for a run up to 100' and my run is only about 34', wouldn't the resistance on that length be less - as indicated actually by the voltage drop calculation?

PMteejk - Re: a sparkie being pretty good at fishing wire. The reason why the sheetrock would have to come down is that the exterior wall with the subpanel is an Insulated Concrete Form wall - no voids to fish in like with 2x construction. The seemingly huge mistake was not putting this wire in conduit - a mistake I won't make again if the wall is coming open, for sure.

I'm totally not trying to be 'textbook' or 'professor-like' on this - I just want to be safe and recognize that the sheetrock work etc will pale in comparison to someone getting shocked (killed) by an improper install.

Everyone's input is HUGELY appreciated. It is clear that you guys know more about this than I do. THANK YOU!

 

[s219]

s219 - You said that wire length has nothing to do with 'allowable' ampacity. Do I correctly understand that then that a #14 wire, for example, that is rated for 15 amps of current, but happens to be at, say, 20' in length, simply cannot handle a, say, 30 amp draw - that it'll turn into a fuse, or minimally run hot and be a fire hazard?

Correct -- the ampacity ratings are based on material, insulation type, bundle/conduit type, etc, such that the wire can handle a certain number of amps and not get hot or melt. The ampacity is also affected by numbers of wires in proximity. So there are often limits to how many wires can be in a conduit or bundled together in a jacket. I have even seen some underground/wet rated wire that will have a different ampacity whether direct buried or in conduit. The end focus always comes down to keeping the wire within the temperature rating of its insulator and conductor materials.