Romex Wire

[stile88]

This was posted before however i cant post in the thread

romex the temp rating for nm-b is 90c but we have to use the 60 degree column for the proper sizing

i have ran into some jobs for example they ran #8 romex from breaker then finished off with emt and thhn to the device on the other end and this is on a 50 amp breaker so my question is this acceptable or should they have went up to 6 for this ???

 

[don_resqcapt19]

If this is for AC equipment, it would be ok if the minimum circuit ampacity is 40 amps or less. Other than things like that, the 8 NM needs to be on a 40 amp OCPD.

 

[winnie]

To expand on what @don_resqcapt19 says, the #8 NM can only be used for at an ampacity of 40A.

For most circuits this leads to a requirement for a 40A breaker or less.

In some circumstances, a 40A rated _conductor_ may be used on a 50A or even larger _breaker_. HVAC equipment with appropriate markings is an example where a breaker larger than the conductor ampacity is kosher.

So the answer to 'Is #8 Romex on a 50A breaker acceptable?' is 'We don't know, what is the circuit feeding?'

Jon

 

[infinity]

I have ran into some jobs for example they ran #8 romex from breaker then finished off with emt and thhn to the device on the other end and this is on a 50 amp breaker so my question is this acceptable or should they have went up to 6 for this ???

If you require a 50 amp conductor this would require a minimum of #6 conductors with NM cable.

 

[stile88]

To expand on what @don_resqcapt19 says, the #8 NM can only be used for at an ampacity of 40A.

For most circuits this leads to a requirement for a 40A breaker or less.

In some circumstances, a 40A rated _conductor_ may be used on a 50A or even larger _breaker_. HVAC equipment with appropriate markings is an example where a breaker larger than the conductor ampacity is kosher.

So the answer to 'Is #8 Romex on a 50A breaker acceptable?' is 'We don't know, what is the circuit feeding?'

Jon

i noticed this on a ev charger feed as one example and i have also noticed this on another job i was at for an oven feed

 

[retirede]

i noticed this on a ev charger feed as one example and i have also noticed this on another job i was at for an oven feed

#8 NM on a 50A breaker is a violation in those 2 examples.

 

[stile88]

#8 NM on a 50A breaker is a violation in those 2 examples.

from my original post i stated that its romex to a certain point then its thhn and emt the inspector for the area says this is fine in the old days the master electricians would always put nm 8 on 50 amp breakers so i need more of a clarification as why this is a violation before i challenge anyone on this.. in all your years as a electrician have you seen number 8 romex burn up on a 50 amp breaker

 

[ActionDave]

Sometime in the late 80's Romex switched to NM-B and it got it's insulation upgraded from 60⁰c to 90⁰. A lot of guys started using the the higher and figured #8 Romex was good on a 50A breaker, just like THHN, but that got slapped down in the next code cycle.

 

[infinity]

#

from my original post i stated that its romex to a certain point then its thhn and emt the inspector for the area says this is fine in the old days the master electricians would always put nm 8 on 50 amp breakers so i need more of a clarification as why this is a violation before i challenge anyone on this.. in all your years as a electrician have you seen number 8 romex burn up on a 50 amp breaker

#8 NM cable has a maximum ampacity of 40 amps. You cannot use a 50 amp OCPD with that #8 on any portion of the circuit.

 

[retirede]

from my original post i stated that its romex to a certain point then its thhn and emt the inspector for the area says this is fine in the old days the master electricians would always put nm 8 on 50 amp breakers so i need more of a clarification as why this is a violation before i challenge anyone on this.. in all your years as a electrician have you seen number 8 romex burn up on a 50 amp breaker

What about the NEC NM ampacity table requires clarification?

 

[stile88]

What about the NEC NM ampacity table requires clarification?

i talked with 3 inspectors and also the town inspector for the area the job was done in and all the inspectors for my area said 8 is fine to put on a 50 and town codes supersede nec so i guess there are exceptions ... and to note each inspector has stated that years ago they used to put 8 on 50 all the time with no issues.. again i really would like to know if any number 8 has burned up or caused damage to the 50 amp breaker this is not nm like years ago its nm-b ... anyways case closed i really dont have a leg to stand on going up against the town inspector if he allows it

 

[infinity]

i talked with 3 inspectors and also the town inspector for the area the job was done in and all the inspectors for my area said 8 is fine to put on a 50 and town codes supersede nec so i guess there are exceptions

Where are you located? Most states have adopted some form of the NEC which this violates. I would really like to see that in writing as an adopted code amendment and not just that's the way we do it around here rule.

 

[Little Bill]

i talked with 3 inspectors and also the town inspector for the area the job was done in and all the inspectors for my area said 8 is fine to put on a 50 and town codes supersede nec so i guess there are exceptions ... and to note each inspector has stated that years ago they used to put 8 on 50 all the time with no issues.. again i really would like to know if any number 8 has burned up or caused damage to the 50 amp breaker this is not nm like years ago its nm-b ... anyways case closed i really dont have a leg to stand on going up against the town inspector if he allows it

Why would you want to go against the inspector if he is allowing something he deemed safe?

 

[roger]

stile88, please update your profile to show occupation and location.

Thank you

 

[HEYDOG]

i talked with 3 inspectors and also the town inspector for the area the job was done in and all the inspectors for my area said 8 is fine to put on a 50 and town codes supersede nec so i guess there are exceptions ... and to note each inspector has stated that years ago they used to put 8 on 50 all the time with no issues.. again i really would like to know if any number 8 has burned up or caused damage to the 50 amp breaker this is not nm like years ago its nm-b ... anyways case closed i really dont have a leg to stand on going up against the town inspector if he allows it

If there happens to be a fire because of using a # 8 Romex on a 50 amp breaker the Electrical Contractor is going to be held accountable not the inspectors!

 

[infinity]

If there happens to be a fire because of using a # 8 Romex on a 50 amp breaker the Electrical Contractor is going to be held accountable not the inspectors!

If there is an adopted local code amendment that allows the #8 NM on a 50 amp OCPD why would the EC be liable?

 

[winnie]

NEC ampacity tables are very conservative, because they need to be applicable in many different circumstances.

The same size wire at the same current will be fine stapled to the bottom of joists, and problematic buried in insulation.

The code is also somewhat probabilistic, going for 'practical safeguarding' rather than perfection.

On top of this, code requirements are often based on old materials, with lots of inertia preventing change.

What this means is that using #8 NM on a 50A breaker is probably safe most of the time. Failures will be rare if ever. But I doubt that the analysis has been done to validate changing the code, and the code says 40A usable ampacity.

My guess is that there isn't an official local amendment allowing #8 NM on a 50A breaker, just that this is something the inspectors routinely pass. Also that this hasn't caused any problems in your area.

Jon

 

[tthh]

My two cents. It's one thing of the inspector if working off an older code version and its one thing if is less of a safety issue, but this ampactiy table hasn't changed in a long time as it relates to that wire type. The code says it is not ok...don't do it...it is a safety thing, even if the code is conservative...which it should be.

 

[winnie]

The other point I forgot to add to my post: imagine a code requirement gave a 1 in 1000000 chance of a damage causing failure over the lifetime of the installation.

Now imagine you violate code in some small way, making the risk 100x worse.

IMHO this sort of violation shouldn't be acceptable, but even then the risk remains small.

Jon

 

[HEYDOG]

If there is an adopted local code amendment that allows the #8 NM on a 50 amp OCPD why would the EC be liable?

I would want a copy of the amendment. The contractor is doing the installation and has the license and also knows that the code says a #8 Romex can not be protected with a 50 amp breaker. If the inspectors works for the government….see how successful you will be filing a claim against them. I do not understand why some are always trying to figure away around code requirements. Use a #6 and charge the customer for it!