max ocpd for electric furnace

Status
Not open for further replies.

danger30

Member
I had a correction on a connection of two new replacement furnaces at a residence. The max ocpd listed on the nameplate was 25A. (2nd circuit) The existing circuit is #10 cu fed from a 30A breaker. The furnaces came equipped with 2P25A breakers. 110.3 was referenced. The AHJ requested I change out the breakers in the panel to 25's. Well, it happens to be a Fed Pac, and the two breakers combined are over 200 dollars. I just don't see the logic. Does the 25A breaker in the furnace not limit the current? Isn't the 30A breaker merely a feeder supplying power to the furnaces ocpd? Does the circuit need to be double protected? If so, why? The only evidence I can find in the book that it is indeed a violation is not from 110.3, but maybe 240.10. "Where supplementary overcurrent protection is used for luminaires, appliances, and other equipment or for internal circuits and components of equipment, it shall not be used as a substitute for required branch circuit protection." What do you all think?
 
If the conductors are protected at their permitted ampacities then the overcurrect device at the equipment can protect the equipment. NEC 2008 422.11 is the correct reference. Sounds like you have a code compliant installation.
 
I agree with Bea. This is no different than an a/c unit being fed with a #10 wire and installed on a 40 amp breaker since the unit has overload protection built in. You essentially have the same setup.
 
I gotta disagree, guys......110.3(B). If the nameplate says 25a max..... as Ronnie Regan used to say, "Well, there you go!"
But, does that refer to the branch circuit's OCP, or the appliance's OCP?

If the appliance has its own 25a OCP, doesn't that cover its requirement?
 
If it's built in to the appliance, it's outside the scope of the NEC, isn't it?

Where is the load? It is after the 25A breaker thus it is protected. The wire is protected via the short circuit and ground fault of the 30 amp breaker. I don't see this as an issue.
 
Where is the load? It is after the 25A breaker thus it is protected. The wire is protected via the short circuit and ground fault of the 30 amp breaker. I don't see this as an issue.

Are the breakers that are in the unit the exact same as what we would put in our panel? Who knows? For all we know, they may only provide overload protection and not short-circuit, or vice-versa. They're not required to be held to NEC standards like the breakers in the panel. What is thier kAIC rating?

I understand your thinking, Dennis. You could have 100 25a breakers and 50 25a fuses built into the unit. But still, if the the label says to protect it with a 25a max breaker, that's what the label says.
 
Are the breakers that are in the unit the exact same as what we would put in our panel? Who knows? For all we know, they may only provide overload protection and not short-circuit, or vice-versa. They're not required to be held to NEC standards like the breakers in the panel. What is thier kAIC rating?

I understand your thinking, Dennis. You could have 100 25a breakers and 50 25a fuses built into the unit. But still, if the the label says to protect it with a 25a max breaker, that's what the label says.


But the breakers are usually standard GE or comparable breakers. I think the nameplate is there in case one would have to replace the breaker. JMO
 
Usually.

So if you see a fuse or breaker in a piece of equipment, then you can ignore the nameplate?


I am not ignoring the nameplate. The fuse or cb in the unit, IMO satisfies the nameplate. Do you really think they would install a specialized CB that didn't give overload as well as ground fault and short circuit protection? All it need is overload protection and I am certain it does indeed give that protection. Have a checked- NO. :smile:
 
Better not be.....(installed)..
I was responding to what I thought was a generic statement.....
more just to mess with you as I enjoy your input & knowledge I couldn't resist....:smile:
 
Why not just install a fused disconnect (fused at 25a) before the unit, fed with the #10 on the existing 30a. brkr. No new brkr to buy, unit now protected at 25a. Everyone goes home happy. :grin:
 
Why not just install a fused disconnect (fused at 25a) before the unit, fed with the #10 on the existing 30a. brkr. No new brkr to buy, unit now protected at 25a. Everyone goes home happy. :grin:
It would be cheaper to just change the breaker in the panel. Besides, as Ken said, I need to break 10,000. Interestingly enough I had no idea I was that close. :smile:
 
Status
Not open for further replies.
Top