# 120/208v on a 4 unit apt. Building



## Skipintime (Mar 25, 2013)

Serviced an apt with a toasted 25 a WH breaker. Found out it had a 120v/208v service. Did load calc. For WH 4500w/208v x 125% got 27 amps. Changed to 30a breaker since it had 10awg and moved to a clean spot on buss. Should I get power co involved to change to a 120/240. Is this acceptable for a 4 unit residential?


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## BBQ (Nov 16, 2010)

Was the element rated 4500 at 208 or 4500 at 240?

As far as a 208 service that is not a problem or odd.


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## Skipintime (Mar 25, 2013)

Yes 4500 for 240 but alt. 3500 for 208 so load would be around 21amps. Would the 208 voltage affect the life or efficiency of the residential appliances/units ?


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## BBQ (Nov 16, 2010)

Skipintime said:


> Yes 4500 for 240 but alt. 3500 for 208 so load would be around 21amps.


That was why a 25 amp breaker was used and a 30 might be a 422.11(E) violation. 



> *422.11 Overcurrent Protection.* Appliances shall be protected
> against overcurrent in accordance with 422.11(A)
> through (G) and 422.10.
> 
> ...



As far as the 208, no it will not shorten the life of appliances. Many water heaters, ranges, heaters, and dryers are actually rated for both 208 and 240 as many thousands of apartment buildings are supplied at 208 volts.


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## Celtic (Nov 19, 2007)

Skipintime said:


> Should I get power co involved to change to a 120/240....


really?


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## Skipintime (Mar 25, 2013)

Celtic said:


> really?


Learning from the experienced electricians here not condescending ones.


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## micromind (Aug 11, 2007)

A 4500 watt 240 volt element will draw 16.25 amps when operated on 208. 220.5(B) allows fractions of less than 0.5 to be dropped from branch-circuit calculations. Therefore, the calculated current would allow a 20 amp breaker and #12 wire. A 25 with #10s would also be permitted. A 30 would be in violation of 422.11(E)(3).

The nameplate lists 3500 watts for 208, which is inaccurate. The true number is 3380. 

Using 3500 watts at 208, the current would be 16.8 amps. #10s and a 25 amp breaker would be needed. A 30 would violate 422.11(E)(3). 

I've seen tons of 4500 watt 240 volt water heaters connected to 208 using #10s and 30 amp breakers though. 

P.S. If a 4500 watt 240 volt element is supplied by 240 volts, #10s are required, but either a 25 or 30 amp breaker is ok.


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## bkmichael65 (Mar 25, 2013)

You can use the higher rating off the nameplate to figure your ampacity rating for conductors and overcurrent as it is rated to handle that amount of current. I would have probably stuck with 25amp breaker, but 30 should be fine


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## BBQ (Nov 16, 2010)

bkmichael65 said:


> You can use the higher rating off the nameplate to figure your ampacity rating for conductors and overcurrent as it is rated to handle that amount of current.


No, you can't use the 240 figures if you are running it 208.



> I would have probably stuck with 25amp breaker, but 30 should be fine


I agree it will be fine but it will be an NEC violation.


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## Celtic (Nov 19, 2007)

Skipintime said:


> Learning from the experienced electricians here not condescending ones.


You have a lot to learn


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## Skipintime (Mar 25, 2013)

Trying, but sometimes feel like giving up. Discouraged!


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## Ultrafault (Dec 16, 2012)

Dont be discouraged you had a good question and now you have a good anwser. We have all had to learn, sometimes the hard way. If you want to know more take classes. Im taking a two semester code class now becuase the last one I took was 10 years ago.


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