Prevention of undersized circuit with over rated device?

[kwired]

The local inspection departments will run buy back programs to get these dangerous items off the streets.

Of course it will be a government subsidized buy back program :happyyes:

remember cash for clunkers?

 

[eoino1]

over load prevention

over load prevention

As long as the circuit protection device is properly sized there should be no significant problems except nussance tripping and overloading the circuit protection. The real problem arrises when undersized equipment is protected by oversized protection an example would be using an old 50amp range circuit to supply a 240v 30amp ac unit . In this case our overload protection is insufficient to protect the equipment and can now be considdered a hazard. Over protection can be a annoying while underprotection can be downright dangerous.

 

[hurk27]

So we must stop putting anymore than one receptacle per branch because that allows people to overload the circuit.

Of course all power strips and three way adapters will also have to be outlawed.

The local inspection departments will run buy back programs to get these dangerous items off the streets.

I agree with what you are saying but 210.21(B)(3) does say for 15 amp circuit that the receptacle is not to be over a 15 amp rating, and 210.21(B)(2) as well as 210.23 clearly does not want us to over load a circuit by limiting the loads to 80% and 50%, which how this can be accomplished after the inspections are done and the green tag has been given is kind of not enforceable in most cases.

We all have seen breakers that you could weld with without them tripping, and we also know that the tripping curve of most breakers would allow a 3 or 4% overload for quite some time before opening, I have even had some new ITE breakers not trip on a fault to which it burned up the NM cable, but like you said an inspector has no way to police what the user does after the inspections are done nor should they as we should not be put in a padded room as we should be allowed to live as dangerously we see fit as long as we don't put others at risk, I had two 20 amp ITE breakers hold with two 1500 watt portable space heaters on the same circuit the only thing that opened was the burned up 15 amp rated receptacle and it wasn't even the one they were plugged into, I replace the breaker twice before I got one that would trip, the home owner told me it worked for over a week like that before the receptacle went bad, but it did scare him so I ran a dedicated circuit for each heater and used industrial grade receptacles.

 

[iwire]

I agree with what you are saying but 210.21(B)(3) does say for 15 amp circuit that the receptacle is not to be over a 15 amp rating, and 210.21(B)(2) as well as 210.23 clearly does not want us to over load a circuit by limiting the loads to 80% and 50%, which how this can be accomplished after the inspections are done and the green tag has been given is kind of not enforceable in most cases.

We all have seen breakers that you could weld with without them tripping, and we also know that the tripping curve of most breakers would allow a 3 or 4% overload for quite some time before opening, I have even had some new ITE breakers not trip on a fault to which it burned up the NM cable, but like you said an inspector has no way to police what the user does after the inspections are done nor should they as we should not be put in a padded room as we should be allowed to live as dangerously we see fit as long as we don't put others at risk, I had two 20 amp ITE breakers hold with two 1500 watt portable space heaters on the same circuit the only thing that opened was the burned up 15 amp rated receptacle and it wasn't even the one they were plugged into, I replace the breaker twice before I got one that would trip, the home owner told me it worked for over a week like that before the receptacle went bad, but it did scare him so I ran a dedicated circuit for each heater and used industrial grade receptacles.

In my opinion we count on breakers to work as they should in every circuit with multiple receptacles. I see no reason at all to treat a 50 amp outlet on a 40 amp circuit any differently.


Lets say I have a cord and plug connected peice of equipment that has an MCA of 70 amps and max OCPD rating of 90.

What size receptacle outlet would you use?

 

[don_resqcapt19]

...I had two 20 amp ITE breakers hold with two 1500 watt portable space heaters on the same circuit the only thing that opened was the burned up 15 amp rated receptacle and it wasn't even the one they were plugged into, ...

Not tripping at that load would be within the requirements of the UL breaker standard. The standard permits breakers to carry 134.9% of their rating forever without tripping. At a 135% of rating, they must trip within one hour.

 

[kwired]

In my opinion we count on breakers to work as they should in every circuit with multiple receptacles. I see no reason at all to treat a 50 amp outlet on a 40 amp circuit any differently.


Lets say I have a cord and plug connected peice of equipment that has an MCA of 70 amps and max OCPD rating of 90.

What size receptacle outlet would you use?

I already tried to say that:

So what receptacle would one use with a circuit that had a 70,80, or 90 amp overcurrent device? Probably not a 60 amp receptacle. Next higher rated receptacle in most instances would be 100 amps. Where does NEC say a device can not have less load/less overcurrent protection then its rating?

 

[hurk27]

In my opinion we count on breakers to work as they should in every circuit with multiple receptacles. I see no reason at all to treat a 50 amp outlet on a 40 amp circuit any differently.


Lets say I have a cord and plug connected peice of equipment that has an MCA of 70 amps and max OCPD rating of 90.

What size receptacle outlet would you use?

I'm not disagreeing with you one bit, just pointing out that the NEC seems to contradict it's self when it tries to impose load limits on circuits in 210.21(B)(2) as well as 210.23, which in many cases are not even enforceable after the inspection has past.

To me these limits should not be in the NEC even if it is a bad design to on purpose design a circuit that will cause the OCPD to neusent trip, but then the NEC claims not to be a design manual?:huh:

From a safety stand point it shouldn't be a problem as long as the OCPD functions as intended.

 

[hurk27]

Not tripping at that load would be within the requirements of the UL breaker standard. The standard permits breakers to carry 134.9% of their rating forever without tripping. At a 135% of rating, they must trip within one hour.

I agree that with the built in underrating of conductors with a little safety head room will in most cases the above will never be a problem, you are more likely to see failures at terminations then to see failure of the wires insulation, but where I do see a problem is when an installer does not take into account of long runs, even a bolted fault can be a problem when the impedance of the circuit limits the current the breaker sees which takes the breaker a longer time to clear which can lead to insulation failure, but this is an installation problem not a code issue.