240.10 Supplementary Overcurrent Protection

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ohmhead

ohmhead

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If I have a VTU mean VAV unit lets say a 20 amp branch circuit with 12 thwn wire on a 20amp 3 phase breaker but the unit only pulls 6 amps and the unit came with its own fused disconnect install by factory . Why do you think the electrical inspector would reject it and use article 240.10 .

I see branch circuit protection with the panel breaker at 20 amps I see the unit protection by its own fused disconnect .

What did I miss ?
 
ActionDave said:
Sounds okay to me.

Is it possible MOCP on the nameplate less than 20A?
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Lets say the MOCP is max 15amp would the fused disconnect be acceptable at 6 amps why would the branch circuit be in the question and what part of 240.10 would limit this . I see equipment protection and I see branch circuit protection .

Factory has a fused disconnect because the wire inside the unit is smaller

Lets look at article 100 A device intended to provide limited protection is it just luminaires or appliances it states equipment also in addition to I see in addition to .

So is this telling me I cant have just the factory protection and must change my breaker in panel I just don't understand the wording and I don't see what is wrong here .
 
ohmhead said:
...I don't see what is wrong here .
Click to expand...
Perhaps the inspector does not understand "supplementary overcurrent protection". Perhaps you don't. We have to establish which... :huh:

Does the factory disconnect have a listing label? Could be that the inspector cannot establish that the disconnect w/fuses is listed for circuit interruption (A.I.C. is part of that). As such, with an MOCP of 15A, that would have to apply to the supply circuit.
 
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If the unit has a maximum over current device label of less than 20 you can't supply it with a 20 amp circuit regardless of any internal fuses.
 
Yes I don't that's why iam asking the question so what I need is a listed factory fused disconnect that has a AIC rating of what .

To match the AIC rating of breaker from panel supply the power to unit .

Also if the unit name plate states MOCP size then any circuit supply must be that max breaker size no exceptions even with a fused disconnect on unit is less than name plate MOCP .Now what if I added a fused disconnect ahead of unit would that be a code issue .
 
If you add OCPD which is listed for use as branch/feeder OCPD, which protects the unit, then you can put it on a larger breaker at the panel.
The wires from panel to added OCPD may need to be large enough to be protected by the panel breaker, or they might be qualified as taps or motor branch conductors.
If the latter they may only need to be large enough to cover the listed MCA of the unit.

Tapatalk!
 
Seems like you are dancing around the issue. Everyone's already contributed their opinions.

Just exactly what are the facts...??? Perhaps the make and model...?

Does the unit have an MOCP on the nameplate? Is it 15A? If not, what is it?
 
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