Do We Protect the 'Load'?

[iwire]

I have noticed quite few recent posts that have stated the following. (more or less)

The branch circuit overcurrent device does not protect the load.

I disagree and offer some code sections to back that up.

422.11 Overcurrent Protection.
Appliances shall be protected against overcurrent in accordance with 422.11(A) through (G) and 422.10.
(A) Branch-Circuit Overcurrent Protection. Branch circuits shall be protected in accordance with 240.4.

If a protective device rating is marked on an appliance, the branch-circuit overcurrent device rating shall not exceed the protective device rating marked on the appliance.

422.11(E) Single Nonmotor-Operated Appliance. If the branch circuit supplies a single non?motor-operated appliance, the rating of overcurrent protection shall

(1)Not exceed that marked on the appliance;

(2)If the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less, not exceed 20 amperes; or

(3)If the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes, not exceed 150 percent of the appliance rated current. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.

What this and other sections say to me is that the branch circuit OCPD is indeed expected to protect the wiring in the appliances.

NEC rules along with the listing agencies requirements combine to keep the wiring in an appliance from melting down before the BC-OCPD operates.

Would any of us think it was safe to feed an appliance that has a 15 amp cord cap with a 50 amp circuit?

[ January 06, 2006, 08:40 AM: Message edited by: iwire ]

 

[bobhudon]

Re: Do We Protect the 'Load'?

Article 422.11 covers appliances. Is there an equivalent for industrial devices (barcode scanners, vision systems, encoders, etc.)?

 

[Jhr]

Re: Do We Protect the 'Load'?

Appliances shall be protected against overcurrent in accordance with 422.11(A) through (G) and 422.10.
(A) Branch-Circuit Overcurrent Protection. Branch circuits shall be protected in accordance with 240.4.

To me it is the appliance and the branch circuit that is been protected, not the load. That been said the appliance produces the load, but when there is an overload then that is when the OCPD comes in to play, to protect the appliance and/or the wiring of the branch circuit from damage.

[ January 06, 2006, 10:00 AM: Message edited by: Jhr ]

 

[iwire]

Re: Do We Protect the 'Load'?

Originally posted by Jhr:

Appliances shall be protected against overcurrent in accordance with 422.11(A) through (G) and 422.10.
(A) Branch-Circuit Overcurrent Protection. Branch circuits shall be protected in accordance with 240.4.

To me it is the appliance and the branch circuit that is been protected, not the load.

OK, lets say it is a motor operated appliance the 'load' is the motor.

Can the branch circuit overcurrent device be used to protect the motor?

422.11(G)
430.32(D)(1)

 

[Jhr]

Re: Do We Protect the 'Load'?

OK, lets say it is a motor operated appliance the 'load' is the motor.

The motor produces the load, and if for some reason there is an overload the OCPD (ie. heaters, breakers) protect the motor and/ or branch circuit from damage.If you put an amprobe on the wires going to the motor and the motor is not on there is no reading/no load, when the motor starts up there is a reading on the meter therefor there is a load on the branch circuit . That is why there is a load calculation that we do in order to make sure the motor, branch circuit are all going to work/do there job when that motor starts up and produces a load.

[ January 06, 2006, 10:31 AM: Message edited by: Jhr ]

 

[bthielen]

Re: Do We Protect the 'Load'?

If the OCPD was intended to actually protect the load itself, wouldn't the wiring in an electric range have to be sized for a 40A or 50A OCPD? The small gauge wiring internal of the appliance is not protected by a 40A circuit breaker so how is the load protected?

Bob

 

[iwire]

Re: Do We Protect the 'Load'?

Originally posted by bthielen:
If the OCPD was intended to actually protect the load itself, wouldn't the wiring in an electric range have to be sized for a 40A or 50A OCPD? The small gauge wiring internal of the appliance is not protected by a 40A circuit breaker so how is the load protected?

Bob

Bob take at look at 240.5(B)(2) and you will see the NEC allowing 50' of 18 AWG to be protected with a 20 amp breaker or 12 AWG to be protected with a 50 amp breaker.

The issue we have to protect the appliance from is short circuits, most times not overloads.