Overcurrent protection

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MiloHEES

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A client is questioning whether the following meets NEC:

48 KW heater consisting of three 16KW delta heaters in parallel, total load 60A
Main feed #4 through 80A breaker and 74A overload
After overloads splits into three short runs of #10 (maximum wire size for heater termination)

The wire is sized per code table 310.15(B)(16) with applicable temperature derate.

I'm thinking section 240.21 allows this based on the short heater tap length.
 
MiloHEES said:
A client is questioning whether the following meets NEC:

48 KW heater consisting of three 16KW delta heaters in parallel, total load 60A
Main feed #4 through 80A breaker and 74A overload
After overloads splits into three short runs of #10 (maximum wire size for heater termination)

The wire is sized per code table 310.15(B)(16) with applicable temperature derate.

I'm thinking section 240.21 allows this based on the short heater tap length.
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What kind of heater is this is so we know what code sections apply to it.

My guess is some sort of process heater more so then space heating?

48 kW @ 460 volts three phase gets you very close to your mentioned 60 A - so I am assuming that is the voltage.

You likely need conductor with an ampacity of 125% of the load which means you need minimum of 75 amp conductor.

Overcurrent protection needs to be 125% also but can use next higher standard overcurrent device.

Sounds so far like 4 AWG and 80 amp breaker are probably fine - but don't know what the application is so can't tell if there is any other detail that may change this.

Not sure why the 74 amp overload is there - should not be necessary.
 
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kwired said:
What kind of heater is this is so we know what code sections apply to it.

My guess is some sort of process heater more so then space heating?

48 kW @ 460 volts three phase gets you very close to your mentioned 60 A - so I am assuming that is the voltage.

You likely need conductor with an ampacity of 125% of the load which means you need minimum of 75 amp conductor.

Overcurrent protection needs to be 125% also but can use next higher standard overcurrent device.

Sounds so far like 4 AWG and 80 amp breaker are probably fine - but don't know what the application is so can't tell if there is any other detail that may change this.

Not sure why the 74 amp overload is there - should not be necessary.
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Yes, sorry - I should have included the 480 volts.
These are process heaters. The unit included a 30 HP fan.
The overloads are included by the manufacturer. Typical for them.

The main issue I am unclear about is the #4 splitting to short runs of #10, and whether additional protection is required for each #10. I recall a 25 foot rule.
 
MiloHEES said:
Yes, sorry - I should have included the 480 volts.
These are process heaters. The unit included a 30 HP fan.
The overloads are included by the manufacturer. Typical for them.

The main issue I am unclear about is the #4 splitting to short runs of #10, and whether additional protection is required for each #10. I recall a 25 foot rule.
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Is this 10 AWG something within a listed assembly? If so NEC doesn't apply - the listing standard for that piece of equipment does.
 
kwired said:
then you need to refer to the applicable listing standard.
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kwired, I have researched UL documents as well as the NEC. It appears that UL refers to NEC.

So, I am back to my original question: does the NEC allow smaller wires to tap into a larger conductor which is protected at 125% of its capacity without OCP for the smaller wires as long as they are 25' or less. In this case we have three #4 protected by 80A breakers and 74A overloads. Can I tap three #10 to each these without further protection as long as the leads are less then 25'?
 
MiloHEES said:
kwired, I have researched UL documents as well as the NEC. It appears that UL refers to NEC.

So, I am back to my original question: does the NEC allow smaller wires to tap into a larger conductor which is protected at 125% of its capacity without OCP for the smaller wires as long as they are 25' or less. In this case we have three #4 protected by 80A breakers and 74A overloads. Can I tap three #10 to each these without further protection as long as the leads are less then 25'?
Click to expand...

Correction: I was just informed these are SPACE heaters.
 
Though it doesn't directly answer your question, take a look at 424.22(B). You might be limited to 60 amps protection on your heating elements at the very least. I see smaller conductors tapped from 50 and 60 amp protected branch circuits within such appliances all the time, not sure what specifically allows it though.

240.5 has some high protection levels for fixture wires - but I don't see that applying to this situation and they don't go any higher then 12 AWG @ 50 amps OCPD. It about has to be something in the listing standards I would think.

424.3(A) does allow fixed infrared heating equipment on a 50 amp branch circuit - doesn't mention anything about making taps from the circuit though.
 
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