80 amp cord on 100 amp plugs, inspector said NO!?

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Waynehof

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Bellingham, Wa
We have 480v 3Ph 62amp portable electric heaters we build for our service work we perform. We work in Industrial facilitys and shipyards. Ive allways built extension cables for this equipment with 100 amp cord ends with type W cable rated at 77 amps.
I install a 80 amp main (or suplemental) breaker in our heater. Its under supervision by qualified persons ect....
The outlet i plug into has a 100 amp CB.
Ive been doing this kind of thing on portable cords for 30 years (doesnt make it right if its wrong..) and never had an inspector say NO.
The other day an inspector quoted 240.5 and said I cant have a 100amp breaker supplying a 77amp cord....

I tried to remember the rule i used for having the 80 amp breaker (in the equipment being serviced) on the 77 amp cord and the rule where i used the suplemental breaker to protect the cord at 80 amps... I couldnt remember, maybe it was from a 1983 code book (lolol).
Am i doing this within an "Exception" type rule or have i been doing this wrong for 35 years....
Thanks for any help.
 
Waynehof said:
We have 480v 3Ph 62amp portable electric heaters we build for our service work we perform. We work in Industrial facilitys and shipyards. Ive allways built extension cables for this equipment with 100 amp cord ends with type W cable rated at 77 amps.
I install a 80 amp main (or suplemental) breaker in our heater. Its under supervision by qualified persons ect....
The outlet i plug into has a 100 amp CB.
Ive been doing this kind of thing on portable cords for 30 years (doesnt make it right if its wrong..) and never had an inspector say NO.
The other day an inspector quoted 240.5 and said I cant have a 100amp breaker supplying a 77amp cord....

I tried to remember the rule i used for having the 80 amp breaker (in the equipment being serviced) on the 77 amp cord and the rule where i used the suplemental breaker to protect the cord at 80 amps... I couldnt remember, maybe it was from a 1983 code book (lolol).
Am i doing this within an "Exception" type rule or have i been doing this wrong for 35 years....
Thanks for any help.
Click to expand...

Electric heaters are generally considered continuous loads. To find the minimum circuit ampacity (the minimum wire size, and the minimum KVA the source needs to be able to supply) you multiply by 1.25.

So 62 amps x 1.25 would be 77 amps. 80 amp wire would be sufficient, but normally needs to be protected by an 80A breaker. For a temporary installation, I'm not sure there is anything wrong with the slightly larger 100A breaker, but I'm not sure it meets the letter of the code either.
 
steve66 said:
Electric heaters are generally considered continuous loads. To find the minimum circuit ampacity (the minimum wire size, and the minimum KVA the source needs to be able to supply) you multiply by 1.25.

So 62 amps x 1.25 would be 77 amps. 80 amp wire would be sufficient, but normally needs to be protected by an 80A breaker. For a temporary installation, I'm not sure there is anything wrong with the slightly larger 100A breaker, but I'm not sure it meets the letter of the code either.
Click to expand...

OP stated he is installing an 80 amp breaker in the heater. Wouldn't that make it good to go?
 
qcroanoke said:
OP stated he is installing an 80 amp breaker in the heater. Wouldn't that make it good to go?
Click to expand...
The common ways that wires are considered protected against overload by OCPD at the far end are when motor wiring rules or tap rules are applicable.
I am not convinced (yet) that an 80A breaker at the load equipment would make the use of 77A portable cord conforming.
 
See following...

240.5 Protection of Flexible Cords, Flexible Cables, and
Fixture Wires. Flexible cord and flexible cable, including
tinsel cord and extension cords, and fixture wires shall be
protected against overcurrent by either 240.5(A) or (B).

(A) Ampacities. Flexible cord and flexible cable shall be
protected by an overcurrent device in accordance with their
ampacity as specified in Table 400.5(A)(1) and Table
400.5(A)(2). Fixture wire shall be protected against overcurrent
in accordance with its ampacity as specified in Table
402.5. Supplementary overcurrent protection, as covered in
240.10, shall be permitted to be an acceptable means for providing
this protection.

(B) ...
Click to expand...

240.10 Supplementary Overcurrent Protection. 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 overcurrent devices or in place of
the required branch-circuit protection. Supplementary overcurrent
devices shall not be required to be readily accessible.
Click to expand...

However, your cord is on the supply side of the supplementary OCP... and does not qualify AFAIK for any of the branch-circuit taps of 210.19(A)(4) Exception No. 1.
 
Last edited:
Smart $ said:
However, your cord is on the supply side of the supplementary OCP... and does not qualify AFAIK for any of the branch-circuit taps of 210.19(A)(4) Exception No. 1.
Click to expand...
'
So a short 100A flexible cord feeding a box containing an 80A CB and that box in turn supplying the 80A rated flexible cord would OK?
 
So, just because I'm confused by this I'll ask...

Why is this 80A cord and 100A plug setup any different from a 16 AWG lamp cord with a male end on it or a 16 AWG extension cord plugged into a 20A 120V receptacle? Are there extenuating circumstances for the smaller circuit cords?
 
PetrosA said:
So, just because I'm confused by this I'll ask...

Why is this 80A cord and 100A plug setup any different from a 16 AWG lamp cord with a male end on it or a 16 AWG extension cord plugged into a 20A 120V receptacle? Are there extenuating circumstances for the smaller circuit cords?
Click to expand...
Yes. Much lower risk to persons and property are the main considerations. Another is NRTL listed equipment is tested for the particular use. YMMV ;)
 
PetrosA said:
Is there a defined cutoff for what amperage circuits can be used with undersized cord sets?
Click to expand...

It is not an undersized cord. It is sized appropriately for the listed conditions of use.

Cords for general service are usually larger so they can accommodate the wider conditions they will see.
 
So the key to 240.5 is "or" Makes sense as you could never overload the supply cord.

240.5 Protection of Flexible Cords, Flexible Cables, and Fixture Wires
Flexible cord and flexible cable, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either 240.5(A) or (B).
 
Smart $ said:
Yes. Much lower risk to persons and property are the main considerations. Another is NRTL listed equipment is tested for the particular use. YMMV ;)
Click to expand...
I would consider the 16 or even 18 AWG zip cord on a 20 amp overcurrent device to be a higher risk for misuse and possible overheating than a 80 amp cord protected at 100 amps.

Would I allow OP's installation? Probably. It kind of is a fine line of whether or not it is a code violation. If he is putting a 100 foot cord on his equipment maybe it should be larger, but if it is only a short cord (I don't know just where to draw the line at length) I don't see a big deal. If he had motors in his equipment he very well may be allowed the higher overcurrent device to allow for motor starting.
 
kwired said:
I would consider the 16 or even 18 AWG zip cord on a 20 amp overcurrent device to be a higher risk for misuse and possible overheating than a 80 amp cord protected at 100 amps.

Would I allow OP's installation? Probably. It kind of is a fine line of whether or not it is a code violation. If he is putting a 100 foot cord on his equipment maybe it should be larger, but if it is only a short cord (I don't know just where to draw the line at length) I don't see a big deal. If he had motors in his equipment he very well may be allowed the higher overcurrent device to allow for motor starting.
Click to expand...
Dang, he's got a good point there.:happyyes:
 
Waynehof said:
We have 480v 3Ph 62amp portable electric heaters we build for our service work we perform. We work in Industrial facilitys and shipyards. Ive allways built extension cables for this equipment with 100 amp cord ends with type W cable rated at 77 amps.
I install a 80 amp main (or suplemental) breaker in our heater. Its under supervision by qualified persons ect....
The outlet i plug into has a 100 amp CB.
Ive been doing this kind of thing on portable cords for 30 years (doesnt make it right if its wrong..) and never had an inspector say NO.
The other day an inspector quoted 240.5 and said I cant have a 100amp breaker supplying a 77amp cord....

I tried to remember the rule i used for having the 80 amp breaker (in the equipment being serviced) on the 77 amp cord and the rule where i used the suplemental breaker to protect the cord at 80 amps... I couldnt remember, maybe it was from a 1983 code book (lolol).
Am i doing this within an "Exception" type rule or have i been doing this wrong for 35 years....
Thanks for any help.
Click to expand...

Who is the inspector and what is he inspecting? Is this a 3rd party inspector hired by the client or is it an electric inspector out of a local building department persuant to a permit?

That heater is industrial equipment/ machinery; it's not a homeowner's furnace. I can't see it needing NRTL.

And being plugged in, doesn't NEC stop at the outlet which is protected by the 100A OCPD?
 
mgookin said:
And being plugged in, doesn't NEC stop at the outlet which is protected by the 100A OCPD?
Click to expand...

At what point does it become necessary to step in and say something different is needed?

How about we put in 100 amp receptacles everywhere and then plug 15 or 20 amp "cheaters" into them for most general use 120 volt equipment? This should greatly reduce chances of so called "nuisance tripping".

After all NEC apparently stops at the outlet.
 
Thanks and questions

Thanks and questions

To clarify a question posted. There was an electrical inspector on site for something else and he happened to walk by where i was working.
He looks over and said that cord isnt large enough to be connected to 100amp breaker..... he sited code and I didnt remember the answers and code Ive used in the past. I remeber now using 240.5 (A)(In red below) and the "supervised industrial location with only qualifed personell" and it worked befor...
So let me review.
240.5(A) Ampacities.
Protection of Flexible Cords, Flexible Cables, and Fixture Wires.
Flexible cord and flexible cable shall be protected by an overcurrent device in accordance with their ampacity as specified in Table 400.5(A)(1) and Table 400.5(A)(2). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table
402.5.
Supplementary overcurrent protection, as covered in 240.10, shall be permitted to be an acceptable means for providing this protection.
So can I apply the statment in red to my heater, in other words my suplementary protection at my heater protects my cable? The branch circuit protection is in place and proper since branch circuit protection ends at the recepticle...
 
kwired said:
I would consider the 16 or even 18 AWG zip cord on a 20 amp overcurrent device to be a higher risk for misuse and possible overheating than a 80 amp cord protected at 100 amps.

Would I allow OP's installation? Probably. It kind of is a fine line of whether or not it is a code violation. If he is putting a 100 foot cord on his equipment maybe it should be larger, but if it is only a short cord (I don't know just where to draw the line at length) I don't see a big deal. If he had motors in his equipment he very well may be allowed the higher overcurrent device to allow for motor starting.
Click to expand...

cowboyjwc said:
Dang, he's got a good point there.:happyyes:
Click to expand...
I agree, the arguments have merit. However, we are bound to the requirements as written.
 
Waynehof said:
...
So can I apply the statment in red to my heater, in other words my suplementary protection at my heater protects my cable? The branch circuit protection is in place and proper since branch circuit protection ends at the recepticle...
Click to expand...
Technically, no. As I stated before, your cord is ahead of the supplementary OCPD.

However, I also noted earlier that it would have to qualify as a tap... but since you mentioned supplementary OCPD from the get go, I had only considered it as a branch circuit "extension" to this point. However, what if we considered this as a feeder tap instead??? I think that would allow the installation as is...
 
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