Hvac

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lmchenry

Senior Member
I am looking at a package unit that has 10kw heat and calls for 63 amp MCA and 80 amp MOCP. If a person were to pull a #4 and protect it with a 80 amp breaker would this violate 424.22 (B)? This is what is on the label. Also, could the loads be separated if the nameplate doesn't give a 2 circuit option?
 

jamesoftn

Senior Member
Location
TN
NEC 2008 424.22
(B) Resistance Elements. Resistance-type heating elements
in electric space-heating equipment shall be protected
at not more than 60 amperes. Equipment rated more
than 48 amperes and employing such elements shall have
the heating elements subdivided, and each subdivided load
shall not exceed 48 amperes. Where a subdivided load is less than 48 amperes, the rating of the supplementary overcurrent
protective device shall comply with 424.3(B). A
boiler employing resistance-type immersion heating elements
contained in an ASME-rated and stamped vessel
shall be permitted to comply with 424.72(A).
 

joebell

Senior Member
Location
New Hampshire
By package unit do you mean a rooftop unit with electric heating as well as cooling? The MOCPD might be based on the cooling compressors also the heating elements maybe seperated inside the unit with fuses to comply.


Joe
 
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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
In this area, we would not allow the 80 amp circuit to go directly to the unit UNLESS the individual protection (not to exceed 60 amps on the heat and the max OCP on the compresssor) was internal to the unit.
Most often here there would be a sub-panel at the package unit (EC installed) with the appropriate OCP for the two loads.
 

lmchenry

Senior Member
Yes it is 240 volt. However, what hangs me up is the fact that the equipment is rated at more than 48 amps and employs such elements as in the second sentence of 424.22b.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
What's the voltage of the unit? 10 KW @ 240 volts is only 41.7 amps.
I am wondering if this is a packaged 10 kw unit with a heat pump similar to the gas packs only with electric heat instead of gas. Then the heat pump may be running along with the heat pump thus the 63 amps.
 

augie47

Moderator
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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Yes it is 240 volt. However, what hangs me up is the fact that the equipment is rated at more than 48 amps and employs such elements as in the second sentence of 424.22b.

Normally, you have the manufacture's option of one circuit or two. If you chose the one circuit option it requires the installation of the mfg supplied fuse kit to protect the load.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
This is probably the case, Dennis. So what do you think?

Given that the heat pump is , in fact, part of the load I am not sure that it would change the requirement of 424.22. Assuming this is a listed piece of equipment then I don't see any other way this could be wired. I would wire it by the nameplate and be done with it.

Are you absolutely certain there is no protection for the heaters inside the unit? I would check out what Augie ( the guy who looks like a dog) said. There may be a kit for the unit
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Given that the heat pump is , in fact, part of the load I am not sure that it would change the requirement of 424.22. Assuming this is a listed piece of equipment then I don't see any other way this could be wired. I would wire it by the nameplate and be done with it.

I see it the same way. Since this is package unit use the information provided by the nameplate as required and hook it up according to the MCA and MAX OCPD info. You could use #6 THHN on an 80 amp OCPD if you so choose.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
my experience has been that if you closley check the fine print in the mfg. instructions, you will find a "sub-fuse kit" is required for "single point connection"
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
my experience has been that if you closley check the fine print in the mfg. instructions, you will find a "sub-fuse kit" is required for "single point connection"


You might be right. So why wouldn't these things come like that from the factory if it's required by the NEC? Is it possible that this is outside of the scope of the NEC?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I think it goes back to most eveything being an option to the "standard" package unit. The heat strip, if any, is flield selected for the installation.
The lit is available when needed. A lot of the installs I see have two seprerate circuits already installed from thel panel to the package location.
Its similiar to the package units with provsions for heat strips being supplied with 60 amp breakers. If a lesser breaker is needed to protect the unit, its a "field" change.

a battle I figfht daily :)
 

lmchenry

Senior Member
Gus, I see the two circuit listing on the nameplate all the time, but this was a carrier unit and it didn't have but one circuit listing. I think I will go back and see what the inside looks like and find out if has provisions inside the unit for separate circuits.
Thanks for the input I will let you know what I find out.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Gus, I see the two circuit listing on the nameplate all the time, but this was a carrier unit and it didn't have but one circuit listing. I think I will go back and see what the inside looks like and find out if has provisions inside the unit for separate circuits.
Thanks for the input I will let you know what I find out.

please do (let us know)
 
This sounds like a manufacturer packaged unit. I would be surprised to see that there is no 'supplementary' OCPDs manufacture installed within the unit.
If you are still unsure, the best bet is to contact the manufacturer. Make sure you get your answer in writing...always helps with the inspector.;)
 

lmchenry

Senior Member
OK, I opened up the unit this morning and this is what I found. First, remember that the label only has a option of one circuit, however there has been two ran to it. Inside the unit there was a fuse bank. Locations for 4 fuses. Two spots for the heating element and two for the compressor. The 2 for the heating was fused at 60 amps and that is what the inside sticker called for. The other two however were not used. They were bypassed. The inside sticker called for a 50 amp on this circuit. But it was run on a #10 on a 30 amp for the compressor. Interesting install.
 
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