Nec

[68electro]

Where in the NEC does it say that a circuit breaker protects wire insulation and not equipment? Thank you.

 

[iwire]

You will not find that in the NEC.

 

[don_resqcapt19]

You can infer from 240.3, that the overcurrent protection rules in Article 240 are not intended to protect equipment.

 

[iwire]

You can infer from 240.3, that the overcurrent protection rules in Article 240 are not intended to protect equipment.

I have to disagree here.

If that where the case there would be no reason at all for maximum overcurrent device ratings on equipment that the NEC requires us not to exceed.

 

[480sparky]

410.153.
422.11.
427.57.
430.95.
440.21.
450.3.
455.7.

All specifically deal with overcurrent protection of something other than conductors.

 

[pfalcon]

You can infer from 240.3, that the overcurrent protection rules in Article 240 are not intended to protect equipment.

I have to disagree here.

If that where the case there would be no reason at all for maximum overcurrent device ratings on equipment that the NEC requires us not to exceed.

240.1 with Footnote:: Conductors and Equipment are covered.
Article 240 covers general overcurrent protection.

240.3 requires using Table 240.3 for equipment listed in the table.
Listed articles in the table replace the general coverage of article 240.

In short:: Use the article listed in Table 240.3 if your device is listed there; Otherwise use article 240.

 

[petersonra]

Where in the NEC does it say that a circuit breaker protects wire insulation and not equipment? Thank you.

I don't recall seeing that anywhere.

In general, the branch circuit OCPD protects the branch circuit. It can also protect equipment, but is not generally required to.

There are cases where it is practical to use the BC OCPD to protect both a BC and some piece of equipment, and there are cases where it is not.

 

[don_resqcapt19]

...
In short:: Use the article listed in Table 240.3 if your device is listed there; Otherwise use article 240.

I don't agree. If the equipment is not covered by the articles listed in T240.3, then the NEC does not directly cover the overcurrent protection of that equipment. Overcurrent protection may be indirectly required by the application of 110.3(B).

 

[don_resqcapt19]

410.153.
422.11.
427.57.
430.95.
440.21.
450.3.
455.7.

All specifically deal with overcurrent protection of something other than conductors.

Yes, and I said that Article 240 only covers the protection of the conductors. The articles you listed do require protection for equipment but those rules are not found in Article 240.

 

[don_resqcapt19]

I have to disagree here.

If that where the case there would be no reason at all for maximum overcurrent device ratings on equipment that the NEC requires us not to exceed.

That would not be an Article 240 requirement. It would be a 110.3(B) requirement.
With the exception of the rule in 240.13, I don't find any rules in Article 240 that require overcurrent protection for equipment.

 

[pfalcon]

I don't agree. If the equipment is not covered by the articles listed in T240.3, then the NEC does not directly cover the overcurrent protection of that equipment. Overcurrent protection may be indirectly required by the application of 110.3(B).

I'll only buy into that if you can explain why and equipment appears in the fine print note for the scope of the article but doesn't really mean it.

240.1 Scope.
FPN: Overcurrent protection for conductors and equipment is provided ...

 

[david luchini]

That would not be an Article 240 requirement. It would be a 110.3(B) requirement.

I don't see in the OP that it asked where Article 240 says that a circuit breaker protects wire insulation and not equipment. It asks where does the NEC say that. I agree with Bob that it does not say that.

With the exception of the rule in 240.13, I don't find any rules in Article 240 that require overcurrent protection for equipment.

What about 240.3? That is a rule in Article 240 that requires overcurrent protection for equipment.

I think you are reading the question as "what article in the NEC requires overcurrent protection for all equipment?" I read it "what article in the NEC says overcurrent protection is not required for any equipment, only conductors."

If you want to get really technical, the OP asks about a c/b protecting "wire insulation." I don't think the code talks about protecting "insulation" anywhere. It talks about protecting "conductors," either insulated, covered or bare.

 

[68electro]

NEC- ocpd for equipment

NEC- ocpd for equipment

Thanks for the replies. I have a client who wants to see a simple explanation in print aside of the NEC. I saw a code article in either EC&M or Electrical Contractor that gave a good explanation of circuit breaker protection.
Does anybody have a recollection of this article. I believe it was this year.

 

[RETRAINDAILY]

Thanks for the replies. I have a client who wants to see a simple explanation in print aside of the NEC. I saw a code article in either EC&M or Electrical Contractor that gave a good explanation of circuit breaker protection.
Does anybody have a recollection of this article. I believe it was this year.

http://ecmweb.com/nec/code-basics/electric_art_overcurrent_protection/index.html

Here is one

 

[iwire]

I have to disagree here.

If that where the case there would be no reason at all for maximum overcurrent device ratings on equipment that the NEC requires us not to exceed.

That would not be an Article 240 requirement. It would be a 110.3(B) requirement.
With the exception of the rule in 240.13, I don't find any rules in Article 240 that require overcurrent protection for equipment.

Don, I do not see anything in the OP that limits us to Article 240.

210.20 seems to tell us we must protect equipment.

If we are not protecting equipment why are there limits to the size of over current devices for say motors 430.52?

Even if I run 400 amp conductors from the source all the way to a 30 amp motor I cannot exceed the ratings shown in T430.52 with my breaker or fuse.

 

[cschmid]

now this is an interesting question..I agree I know of no area it says that over current is for wire insulation..Yet it is interesting that we create a 20 amp circuit and every part of that circuit is 20 amp rated and there is no equipment designated for the circuit; so what are the requirements if not the protection of wire and devices? it can not be the equipment as there is no equipment on the circuit. interesting topic yet the code does not state wire insulation.

 

[Cold Fusion]

Guys -
There is very little in the NEC about circuit breakers protecting equipment because they don't do that.

I can only think on one case where a CB actually does protect the conductors - circuits with multiple receptacles. Ten 120V, 15A receptacles on a 20A circuit could have 20 - 1500w hair dryers plugged in. 30 kw would likely trip the CB fairly quickly :roll:

So setting that one case aside for the rest of the post:

The CB protects the structure. It is there to put out the fire after something fails. It doesn't prevent failures.

Here's an example. Motors are protected by design - Not the CB, not the overloads. If the motor internally faults, there is no motor to save - it's dead. So while the motor is busy doing it's Chernobyl act. The cb trips to keep the conductors from melting down and starting a fire. Supposing the motor bearings fail and the motor loading goes up to where the motor is overheating. The over loads should take it out. Saved the motor - right? Yes they did. Until some goof repeatedly resets the overloads ..... sigh - now the CB comes into play to shut down the fire.

Here's another one - perhaps my favorite. Outside unlimited taps on a xfm secondary:
Them: What protects the transformer and conductors from overload?

Me: Well the design does. Perhaps your asking what protects the transformer from a downstream fault? The secondary OCP about 1000 feet yonder. The current that leaves the transformer has to come out the CB end.

Them: Supposing there is an overload between the transformer and the First OCP?

Me: Ah. You mean like a backhoe attack. In that case there are no conductors to protect - they are dead. Now the issue is to get the transformer off line before it fails. The primary OCP should be designed to do that. By the way, the NEC limits may not do that.

If you wish to protect the conductors, try concrete and steel - not a CB

cf

 

[iwire]

CF I cannot see it that way as often equipment or conductors are overloaded and the breaker opens before more damage happens,

Example: Branch circuit wiring is overloaded, breaker opens before the conductors become damaged. Remove overload reset breaker and we are back in business. The breaker protected the conductors from damage.

Example; a motor is mechanically held up, the overloads open before the motor is damaged the OLs protected the motor from damage.

 

[Cold Fusion]

CF I cannot see it that way as often equipment or conductors are overloaded and the breaker opens before more damage happens,

Example: Branch circuit wiring is overloaded, breaker opens before the conductors become damaged. Remove overload reset breaker and we are back in business. The breaker protected the conductors from damage.

Example; a motor is mechanically held up, the overloads open before the motor is damaged the OLs protected the motor from damage.

And I dealt with both of those scenerios in my post. Did you miss that?

cf

 

[petersonra]

There are really two things that need to be protected against that a CB could provide protection for. One is short circuit, and the other is overload. In most cases the CB provides protection to the BC conductors for both of these issues, but not necessarily for the device under power.

The BC CB generally only protects motors against short circuits, and overload protection is supplied by some other means.

Must plug and cord connected appliances found in residential use either have some form of internal OL protection, or none. The BC CB does not typically provide any OL protection for them, but does provide SC protection.