Breaker sizing

H

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
I have instantaneous water heater non continuous load 4160 watts at 208V single phase and has full load amps of 20A.

The engineer has provided 25A breaker size. When asked why he says he was taking into 80% breaker rating.

I thought if its non continuous load the breaker needs to be 20A, 100% of full load amps. Now I am confused should it be 20A or 25A?
 
hhsting said:
I have instantaneous water heater non continuous load 4160 watts at 208V single phase and has full load amps of 20A.

The engineer has provided 25A breaker size. When asked why he says he was taking into 80% breaker rating.

I thought if its non continuous load the breaker needs to be 20A, 100% of full load amps. Now I am confused should it be 20A or 25A?
Click to expand...
It could be either.
 
Minimum breaker size would be the load amps and rounded up to the standard size. Many appliances can have a breaker size up to 150% of nameplate unless marked otherwise (422.11(E)). So he could put it on a 20, 25, or 30A breaker. Need to watch 240.4(D) though. If he uses a 25A breaker, the circuit will need #10 wire.
 
suemarkp said:
Minimum breaker size would be the load amps and rounded up to the standard size. Many appliances can have a breaker size up to 150% of nameplate unless marked otherwise (422.11(E)). So he could put it on a 20, 25, or 30A breaker. Need to watch 240.4(D) though. If he uses a 25A breaker, the circuit will need #10 wire.
Click to expand...

Even for non continuous load??? The instantaneous electric water hearer is non continuous.
 
Yes. Permitted doesn't mean you have to do it. It is an allowance that could be useful. But 20A is the minimum and 30A is the maximum. Just like a breaker on an HVAC unit -- it has to be between MCA and Max breaker -- any size is allowable as long as it is between those extremes.

If this was a continuous load, then he would have to use a 25 or 30A breaker, or find a 100% rated breaker in 20A which probably doesn't exist.
 
hhsting said:
Even for non continuous load??? The instantaneous electric water hearer is non continuous.
Click to expand...
For non-continuous the branch circuit in this case can be 20, 25, or 30 amps. The conductor size would need to be at the minimum the OCPD size. If the engineer specified 25 amps you're only concern is the correct conductor size.
 
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