Ask Me Help Desk - Hot tub 240 volt wiring

Hot tub 240 volt wiring

I am wiring a hot tub. I have a 50ft run from the circuit breaker panel to the hot tub CGCI box, and another 35ft from the GFCI box to the hot tub. The specs call for a 50 amp 4 wire system. My question is, what size wire should I use? # 6 #8 ?

This is a good diagram -- Hope it helps

Seimens GFCI wiring

The distance of the run will have the largest impact on the choice of wire size.

Consult your local codes to make the appropriate decision.

SpaSupport: Electrical Installation, 230 Volt Spa/Hot Tub

Quote:

Originally Posted by Drillsgtmg

I am wiring a hot tub. I have a 50ft run from the circuit breaker panel to the hot tub CGCI box, and another 35ft from the GFCI box to the hot tub. The specs call for a 50 amp 4 wire system. My question is, wat size wire should I use? # 6 #8 ?

This depends on the inside wiring portion. If it is NM cable then you must use #6. If the run will be ALL in conudit then you can get away with #8.
For the outside portion of the wiring to a hot tub or spa you have NO choice but to run conductors in conduit with an insulated ground.

I hope you know all the other important codes with regard to wiring a spa...

Your disconnect must be "line of sight". Is it? 35' seems excessive.

From PM:

Quote:

Originally Posted by Drillsgtmg

This is the message:

I am wiring a hot tub. I have a 50ft run from the circuit breaker panel
to the hot tub CGCI box, and another 35ft from the GFCI box to the hot
tub. The specs call for a 50 amp 4 wire system. My question is, wat
size wire should I use? # 6 #8 ?

The tub is going in a basement and the 35 ft is from the spa box on one
wall , overhead, and down the oppisite wall to the hot tub. Would
braid wire be better?

#4 for 50 Amp continuous load (operates more than 3 hours). This will give you a 2.8% voltage drop or 3.3 volts. This is below the 3% required.
The grounding conductor could be less - not sure how to size.

Stranded won't make any difference.

This is not a 50A continuous load. It is a 50A circuit.

Use #6 cable. Either 6/3 or 6/2 depending on whether the tub requires a neutral.

OK, for a 40 amp continuous load (0.8*50), #6 will give you a 2.8% voltage drop. If the continuous load is less than 40A, then use #6.

To get the continuous load rating, you multiply by 1.25. So 40 * 1.25 = 50 A.

What are you basing your VD numbers on?
85' is not really that far to even be worried about VD.

170', #6 Copper, 120 V.

We don't know what the nameplate says. Without that information, you can go either way in terms of sizing. In the latter case, the breaker could not support a 50 A load continuusly.
Once you have the load, do the vd calcs. Then the CB can be upsized accordingly. There is a motor load involved and I wasn't paying attention to that.

I do believe you are right that, for instance, a 15A 120V circuit should only be loaded to 80% capacity if operating continuously.

Quote:

Originally Posted by KeepItSimpleStupid

170', #6 Copper, 120 V.

This totally NOT the correct way to figure VD in a 240v circuit.
If the circuit is 240v then you use 240v, NOT 120v times double the distance.
One reason for this is because a 240v circuit has substantially less voltage drop than a 120v circuit.

Quote:

Originally Posted by KeepItSimpleStupid

Once you have the load, do the vd calcs. Then the CB can be upsized accordingly.

You mean the wire size would be upsized, right? The CB would stay the same regardless of VD.

I disagree, because he said a 4 wire 240 V circuit, that means the Vd is calculated for the legs or 120 V. Agreed, that N carries the difference current, but if all 40 A was on L1 and L2's load was 0.1 A, what voltage would you use to calculate Vd. N would be 39.9 A.

No, say for instance the caclulated current is 47 A. You can upsize to the next size breaker of 50A, since a 47 A breaker is not available.

Quote:

Originally Posted by KeepItSimpleStupid

I disagree, because he said a 4 wire 240 V circuit, that means the Vd is calculated for the legs or 120 V. Agreed, that N carries the difference current, but if all 40 A was on L1 and L2's load was 0.1 A, what voltage would you use to calculate Vd. N would be 39.9 A.

Come on now. If you've ever wired a hot tub, or any other 120/240v appliance, you'd know that the VAST majority of the load is 240v. The 120v portion of the load is negligible. Besides, any 120v loads would be at least (tried to) be balanced by the manufacturer.

I guess you can do it your way and I'll do it mine.

I didn't imply my example was a hot tub. It was purposely far etched to illustrate a point.

So, how might you size a service entrance cable? Assume that L1 and L2 are nearly balanced and use 240 V?

At least you get the idea. The point is: We don't know the load.

Quote:

Originally Posted by KeepItSimpleStupid

So, how might you size a service entrance cable? Assume that L1 and L2 are nearly balanced and use 240 V?

According to the code and what the POCO requires. As you said, we don't know the load, but yes, I'd use 240v.

Besides, VD is NOT a code issue. There is nothing code enforceable about VD. It is simply a design/performance issue.

I refer you to tkrussel's post who says you need to check both:

https://www.askmehelpdesk.com/electr...on-166806.html

But, then if you do it for the lower voltage, it should be OK for the higher one.

I mean no disrespect, but TK saying you need to check both holds just as much water as me saying you do not.
Then again this is just my own opinion on the matter.

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