I called the manufactures rep. because in their equipment cut sheet for a hot water tank was 20A-2p c/b for 4160 watt 208v. I explained to her that a good engineering practice is that most c/b should be loaded at 80% of their rating. Can I use a 25A c/b. She said that the unit is UL rated non-continuous so that 20A was all it needed. She also mention that breakers in the last nine years have changed so that you can load them up to 100%. I heard of 100% breakers but don't you have to spec them for the equipment or job. Does all breaker now capable of 100% load?
circuit breaker issue
- Thread starter jrvazzer
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Wow, it is of my opinion what she said is bogus. She is typical of the those that are being hired, the blind leading the blind. No, things have not changed. Breakers protect wire unless the manufacturer of the equipment specifies an specific OCPD.
If you are protecting wire the wire is sized to carry 125% of the continuous load + 100% of the non continues load. The wire size selected most be sized to carry the load.Then you select the size of the OCPD to protect the wire. As such the breaker selected will be based on 80%. Yes, there are 100% rated breakers BUT they are only available in the larger breaker fame sizes because it is impractical is apply them in smaller frame sizes. In addition, there is a specific procedure the is used to size the wire, the type if wire, and the enclosure that the 100% rated breaker is mounted in in order to even apply a 100% rated breaker at 100%.
Simply didn't complicate things. Just size the wire to carry the load and protect the wire based upon the wire size or size the breaker based upon what phase been speced by the water heater manufacture.
Thanks. I agreed with everything to wrote. But is the last thing you wrote which I believe requires me not to question. ("size the breaker based upon what phase been speced") It the manufact. equipment sized it and is part of the equip. plate or tag, we must respect it or some inspector can possibly right you up.
I scewed up. "Phase"makes no sense. I should have said "that has been speced by the equipment mfg." If the wire has been sized to carry the load per the NEC then a OCPD selected per the mfr specification as long as doesn't what is required to protect the wire. If the wire is 12ga required to be protected with a 20at OCPD per the NEC the equipment mfg may spec a 15at OCPD the way that I understand it.
Excuse me your saying if the equipment is rated, looking at the cut sheet. Rated at 2080 watts and the manufactures recommends for the maxium over current protection (mocp) is 15Amps your not going question it?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Damn, beat me to it. I had almost the EXACT same response typed out, then the phone rang and I got busy, so it sat open for a few hours. Luckily I decided to double check before posting and sure enough, you were there.
:thumbsup:
This issue is by the way, VERY commonly misconstrued.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Art. 422.11(E) is what you use for sizing the overcurrent protective device. 4160/208= 20amps times 125% = 25 amps. You can use a 25amp or 30 amp breaker since 150% of 20 is 30amps
- Location
- Illinois
- Occupation
- retired electrician
All breakers are tested at 100% load, but they are not tested in an enclosure where they would be exposed to additional heat from other breakers. The 80% is an allowance for the heat from the other breakers to prevent nuisance trips. That being said, it is not uncommon to find standard breakers, even in an enclosure that will carry over 100% of their rating forever. The breaker standard permits the breakers to carry 134% of the rating forever.
- Location
- Illinois
- Occupation
- retired electrician
UL tells us that all of the information supplied by the manufacture is 110.3(B). The use of the 25 or 30 amp OCPD in this case would be a code violation.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
But the manufacturer also stated this by the OP:
Which would conflict with 422.13. No?:?
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
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
What she tells you verbally does not count for 110.3(B). Trust me, I learned that lesson the hard way...
110.3(B) is referring to PUBLISHED manufacturer's data.
110.3(B) is referring to PUBLISHED manufacturer's data.
Thanks for the Refer. Thanks all of you
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
It has always been that way. A 20 amp breaker can handle a 20 amp load as long as the the load is NOT continuous. 210.20(A)
IMHO if the water heater is constructed in such a way that the load does not exceed the circuits ampacity rating, and the load is on some sort of timer, and the Manufacturers instructions dictate a certain size OCPD. then its ok.
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