water heater ?

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neal

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The load is a 24KW 208 water heater.
Amp 66.6 X 125%=83.25 min. wire size.
66.6 X 150%=99.9 max. breaker size.
Exception to rule can go to next standard
size breaker. Contractor installed 100 amp
breaker #2 aluminum with 100 amp disconnect
next to water heater.
Another inspector will not pass this job,
he wants it on 90 amp breaker.
I feel that the contractor has met the code,NEC.

[ February 21, 2005, 12:20 AM: Message edited by: stevearne ]
 
Re: water heater ?

To expand on Bob's answer, table 310.15(B)(6) is only good for it's stated purpose: 120/240 Single Phase Dwelling Unit Services and Feeders. Not meeting any one of these criteria voids the use of the table.

The water heater is on a branch circuit, and more importantly, is 208 volts.

Sometimes around here in certain jurisdictions, a multifamily dwelling is zoned a commercial building. :)

[ January 26, 2005, 09:03 PM: Message edited by: georgestolz ]
 
Re: water heater ?

Originally posted by neal:
240.2 tells us to use article 422,then went to 422.10 and 422.11,e,3
Click to expand...
Hi Neal, I think you mean 240.3?

240.3 Other Articles.
Equipment shall be protected against overcurrent in accordance with the article in this Code that covers the type of equipment specified in Table 240.3.
Click to expand...
Yes, that tells us to use 422 for protection of equipment.

I agree that the breaker size of 100 complies with the equipment protection requirements of sections 422.13 and 422.11(E).

That does not change the requirements of 240.4 Protection of Conductors.

240.4 Protection of Conductors.
Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).
Click to expand...
2 AWG has a rating of 90 which is a standard size, you can not bump up the OCP to 100 for 2 AWG and be in compliance with 240.4.

I doubt it would burn down but in my opinion it is a violation.
 
Re: water heater ?

Wow, that is some hot water heater! What are they heating a lake? Most residential and commercial hot water heaters I have seen have 4500 watt elements in them and they are normally wired for non simultaneous operation so that the top element heats up first and the thermostat is satisfied it allows the bottom element to come on. Also, I seem to remember a statement of using only copper wires with them. I have never run anything larger than a #8 copper and in most cases a #10. Given the benefit of doubt, if this is a heater for the purpose of sterilizing dishes in a commercial kitchen, I still believe the elements are separated into smaller loads are they not? Hell 24Kw is a lot of power for one appliance! According to art 338 and subsequently 334, the ampacity of type SE cable is limited to the ampacities in table 310.16 for either 60 degree C or 75 degree C cables. Also, the cables have to have a temperature limitation in accordance with the type appliance they are feeding.
 
Re: water heater ?

Ben There is strong possibility that this is a commercial water heater, the water temperature may be no higher than a home unit. The high wattage is usually to provide a quick recovery time.

I recently installed a 120 gal electric water heater for some showers.

It had at least 6 maybe 8 (?) elements, that could run simultaneously which totaled 36,000 watts.

We ran it at 408 volt 3 phase which required 6 AWG. At 208 volts 3 phase it would have been about 100 amps.

From cold to hot in a very short time. :D

EDIT; That would be 480 not 408.

[ February 18, 2005, 02:42 AM: Message edited by: iwire ]
 
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