5000W Water Heater

[chris kennedy]

I may have an issue. I have 10 residential units that call for water heaters with 5kw elements. Service is 208y/120.

I get as per 422.13:

5000?208=24.038A

24.038?1.25=30.047

Units are wired in NM. As per 334.80 I see 30A in the 60?C column of T310.16 for #10 NM.

Slightly over the allowable ampacity of the 10/2 mn that is installed.

Am I mistaken?

 

[480sparky]

Is the 5000w divided between two elements, and only one will be on at any given time?

 

[chris kennedy]

No sir, they have two 5000W non-simultaneous elements.

 

[Pierre C Belarge]

Did you read 220.5(B)?

I am not sure if this section number can be applied to 422.13

 

[nakulak]

5000/(208x1.73) ?

 

[JohnJ0906]

Did you read 220.5(B)?

Beat me by a minute!

I am not sure if this section number can be applied to 422.13

I don't see why not. 220.1 says that section 220 applies to branch circuit, feeder and service calculations.

 

[Jljohnson]

Did you read 220.5(B)?

I am not sure if this section number can be applied to 422.13

Good call Pierre. I wouldn't have thought of that seldom used piece of information and pulled 8 copper to the units. You just saved Chris' bacon (or substituted a sirloin steak for his bacon) on that job.

 

[chris kennedy]

5000/(208x1.73) ?

Long story but I have 3? meter stacks serving single phase dwelling units.

 

[480sparky]

5000/(208x1.73) ?

208 is not 3-phase.

 

[chris kennedy]

Did you read 220.5(B)?

I am not sure if this section number can be applied to 422.13

I'm not doing a load calc, I'm sizing a branch circuit. How would that apply?

 

[nakulak]

208 is not 3-phase.

208 is not 3 phase? dang I guess I better quit this trade and do something else.

 

[480sparky]

208 is not 3 phase? dang I guess I better quit this trade and do something else.

You need three wires for 3-phase. You've only got two, so it's single-phase.

 

[chris kennedy]

208 is not 3-phase.

Is the cold getting to you?

Service is 208y/120.

You still have a chance to come down and babysit this one for me.:smile:

 

[480sparky]

Is the cold getting to you?



You still have a chance to come down and babysit this one for me.:smile:

Try making a 3-phase motor work with two hot wires.

 

[chris kennedy]

Try making a 3-phase motor work with two hot wires.

Maybe tomorrow, I'm a little busy today trying to make a 5000W water heater work on #10 NM at 208V.

 

[JohnJ0906]

I'm not doing a load calc, I'm sizing a branch circuit. How would that apply?

Check out 220.1

 

[chris kennedy]

Check out 220.1

Yes sir that is a good one.:smile: But again how does that apply to sizing a branch circuit:-?

 

[JohnJ0906]

Yes sir that is a good one.:smile: But again how does that apply to sizing a branch circuit:-?

220.5(B) applies to branch circuit calcs, because 220.1 says so. :wink:
If you come up with 30.047 amps, you can drop the .047 amps, and use 30 amp conductors.

 

[chris kennedy]

220.5(B) applies to branch circuit calcs, because 220.1 says so. :wink:
If you come up with 30.047 amps, you can drop the .047 amps, and use 30 amp conductors.

When doing a load calc I will drop the fraction, when sizing a branch circuit I will follow this:

422.13 Storage-Type Water Heaters.
A fixed storage-type water heater that has a capacity of 450 L (120 gal) or less shall be considered a continuous load for the purposes of sizing branch circuits.
FPN: For branch-circuit rating, see 422.10.

 

[JohnJ0906]

When doing a load calc I will drop the fraction, when sizing a branch circuit I will follow this:

Those articles are not mutually exclusive.

IMO, 220.5(B) applies to all branch circuit calculations.