I need some clarification please. I am going to install a disconnect for an HVAC contractor. The disconnect will feed a 10kw heat strip, which by code is a continuous use application, so I will be using 6 awg wire and a 60 amp breaker. But the 10kw heat strip got me thinking about the type of disconnect I need. Are all non fusible disconnects able to handle a continuous load from a 10kw heat strip? Is there a wattage limit on disconnects? Am I over thinking this?
10kw heat strip disconnect
- Thread starter SHAEF-Ike
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I never checked but we always used 60 amp disconnects because the wattage is somewhere around 40-45 amps so that is not an issue. BTW, are you using nm cable or another wiring method.
You might want to get some clarification.
IF the circuit is feeding only a heat strip most are actually 9.6kw for a load of 40 amps requiring a 50 amp circuit (125%) BUT if the circuit is feeding the blower motor in addition to the heat strip the minimum circuit can often exceed 55 amps, the ampacity of a #6 NM.
IF the circuit is feeding only a heat strip most are actually 9.6kw for a load of 40 amps requiring a 50 amp circuit (125%) BUT if the circuit is feeding the blower motor in addition to the heat strip the minimum circuit can often exceed 55 amps, the ampacity of a #6 NM.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The 60 amp disconnect is fine
I agree with Gus here that the #6 may not be large enough since you must use the 60C col. for nm cable. Most 10 kw units I have seen draw 56-57 amps which means #6 wont work.
I did get clarification, the #6 is only going to supply the heat strip and not the blower! Thx for watching out folks!
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
huh---I have never heard of that
Agreed. Where would the fan motor get it's power from If not from the circuit supplying the heat strips? It would have to have another circuit just for the fan motor.
Buck Parrish
Senior Member
- Location
- NC & IN
Yes, Most every one uses 60 amp disconnects. It's a very common install.
Fan motor was installed prior to my involvement and is on a 30 dual pole circuit.
it is separate.
Buck Parrish
Senior Member
- Location
- NC & IN
I'm thinking you must be installing heat strips on an existing furnace. It may have been gas before or even just a heat pump or since it's fed by a 2 pole 30 it may have been a 5 kw. Just guessing.
This is an add on to a heat pump.
Can anyone tell me is GFCI is required by NEC for this heat strip? It is in a unfinished basement. Tennessee has not adopted the 2020 code yet so the “outdoor” does not apply. I cannot seem to find in the 2017 code a requirement for GFCI on heater. Is the resistant heater going to trip the GFCI constantly if it is installed? Real frustrating trying to find answers!
Can anyone tell me is GFCI is required by NEC for this heat strip? It is in a unfinished basement. Tennessee has not adopted the 2020 code yet so the “outdoor” does not apply. I cannot seem to find in the 2017 code a requirement for GFCI on heater. Is the resistant heater going to trip the GFCI constantly if it is installed? Real frustrating trying to find answers!
Buck Parrish
Senior Member
- Location
- NC & IN
IMO 2017 does not require gfci for your install.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Agreed no gfci required assuming it is not cord and plug
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
A fan motor would not need dp 30 amps. Something is not right about what you are saying however no gfci is needed in any case
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
maybe a fan and a compressor.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
Instead of a disconnect Square D has those little breaker boxes for a two pole like you use on outdoor condensing units. The "breakers" with no overcurrent protection would work
Hey folks! I am now going to be installing a disconnect and Circuit Breaker (CB) for a 15KW heat strip (heat strip only, no other load). Previous electrician ran a 2 cdr 4 awg 1 cdr 6awg NM copper wire for this install. The heat strip is actually 14,400 watts 208/230 volt. I calculated the CB as 14,400/240 = 60A x 1.25 = 75A so I am using an 80A breaker.
So again my question is 'What size non fused disconnect do I need to install?' Can I use a standard 60A disconnect down stream of an 80A breaker?
So again my question is 'What size non fused disconnect do I need to install?' Can I use a standard 60A disconnect down stream of an 80A breaker?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
No you need a 100 amp disconnect.
The heat strip cannot be 14,400 watts at both 208 and 230 volts.
The heat strip cannot be 14,400 watts at both 208 and 230 volts.
It might be worth your time to make sure there is internal fusing. The Code limits OCP for heating elements to 60 amp so you might end up with a small loadcenter.
There should be a nameplate showing MCA and MOCP for one circuit or two
There should be a nameplate showing MCA and MOCP for one circuit or two
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