Are service breakers de-rated ?

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Peteschmidt

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My primary question is whether it's acceptable to install a 175A continuous rated meter extender in a 200A rated base and a 200A service panel main breaker.

The NEC states that Branch Circuit and and Feeder overcurrent protection must be 125% of expected load, or essentially derated to 80% of it's rating (ref. 215.3 Overcurrent Protection of feeders), but I can't find anything so clear on the sizing service entrance overcurrent protection. Article 220 Parts III and IV lump service and feeder overcurrent calculations in to the same methods, so it stands to reason that they'd have the same derating implied... it just doesn't say so for service breakers (that I can find)

UL489 (the standard used to List circuit breakers for branch circuit, feeder and service entrance overcurrent protection) states in 9.1.4.4 that "A circuit breaker, having a frame size of 250 A or greater, or a multi-pole type of any ampere rating rated over 250 V; and intended for continuous operation at 100 percent of rating, shall be marked:
?Suitable for continuous operation at 100 percent of rating only if used in a circuit breaker enclosure Type (Cat. No.) ____ or in a cubicle space ___ by ___ by ___ mm (inches)?. Equivalent wording shall be permitted. Location Category C. The blanks are to be filled in with the minimum dimensions."

Typical residential 200A service panel main breakers are not marked for 100% (verified on Square D QO and Homeline, Cutler-Hammer panels), so by omission of a 100% marking appear to require 80% derating.

It seems to me, therefore, that the maximum acceptable continuous load on a 200A service would be 160A, therefore using a meter extender rated for 175A continuous use should be acceptable. (note: UL 414 meter sockets and extenders standard allows for an intermittent rating of not more than 125% of the continuous rating with no testing required)

Is there any clear direction in the NEC that requires 80% derating of service breakers for the total load on the panel?
Would code prevent installing a 175A continuous meter extender in a 200A service?

Thanks!
Pete
 
Peteschmidt said:
...

Is there any clear direction in the NEC that requires 80% derating of service breakers for the total load on the panel?
Would code prevent installing a 175A continuous meter extender in a 200A service?
Click to expand...
Welcome... :thumbsup:

To state panel main breakers are derated is quite onerous. Except for specific atypical cases, panels seldom supply all continuous loads. They can supply up to 100% of their rating with noncontinuous loads (as calculated).

In the case of service breakers, their "derating" is indirectly implied/inferred :)D) from the minimum ampacity requirement of the service conductors {310.15(B)(7) being an exception}. Refer to 230.90.

I'm not sure what a continuous meter extender is. Please explain...
 
Smart $ said:
I'm not sure what a continuous meter extender is. Please explain...
Click to expand...

"Continuous" referred to the rating of the extender... it's rated 175A continuous.

The meter extender is to space the meter out from the meter base. In this case, it's being installed to tap power at the meter to power Listed communications equipment as allowed by 230.82 (9).
 
Peteschmidt said:
My primary question is whether it's acceptable to install a 175A continuous rated meter extender in a 200A rated base and a 200A service panel main breaker.

...
Click to expand...

Peteschmidt said:
"Continuous" referred to the rating of the extender... it's rated 175A continuous.

The meter extender is to space the meter out from the meter base. In this case, it's being installed to tap power at the meter to power Listed communications equipment as allowed by 230.82 (9).
Click to expand...
IMO, it would not be acceptable unless you also downsized the panel main breaker to 175A... calculated load permitting.
 
Peteschmidt said:
My primary question is whether it's acceptable to install a 175A continuous rated meter extender in a 200A rated base and a 200A service panel main breaker.

The NEC states that Branch Circuit and and Feeder overcurrent protection must be 125% of expected load, or essentially derated to 80% of it's rating (ref. 215.3 Overcurrent Protection of feeders), but I can't find anything so clear on the sizing service entrance overcurrent protection. Article 220 Parts III and IV lump service and feeder overcurrent calculations in to the same methods, so it stands to reason that they'd have the same derating implied... it just doesn't say so for service breakers (that I can find)

UL489 (the standard used to List circuit breakers for branch circuit, feeder and service entrance overcurrent protection) states in 9.1.4.4 that "A circuit breaker, having a frame size of 250 A or greater, or a multi-pole type of any ampere rating rated over 250 V; and intended for continuous operation at 100 percent of rating, shall be marked:
?Suitable for continuous operation at 100 percent of rating only if used in a circuit breaker enclosure Type (Cat. No.) ____ or in a cubicle space ___ by ___ by ___ mm (inches)?. Equivalent wording shall be permitted. Location Category C. The blanks are to be filled in with the minimum dimensions."

Typical residential 200A service panel main breakers are not marked for 100% (verified on Square D QO and Homeline, Cutler-Hammer panels), so by omission of a 100% marking appear to require 80% derating.

It seems to me, therefore, that the maximum acceptable continuous load on a 200A service would be 160A, therefore using a meter extender rated for 175A continuous use should be acceptable. (note: UL 414 meter sockets and extenders standard allows for an intermittent rating of not more than 125% of the continuous rating with no testing required)

Is there any clear direction in the NEC that requires 80% derating of service breakers for the total load on the panel?
Would code prevent installing a 175A continuous meter extender in a 200A service?

Thanks!
Pete
Click to expand...

When the NEC doesn't specifically address overcorrect/overload protection of a piece of equipment, it is unclear how you take the equipment's rating into account. For example, take a 100 amp meter socket and put it on a 200 amp service. Ok or not? What if the calculated load is under 100 amps? Or take a cold sequenced meter stack with a bus rating of 1200 amp and put it after a 1600 amp OCPD. Ok? What if NEC calculated load was over 1200 amp but actual load is under 1200 amps?
 
I think they are for extending a meter to allow other device attachments such as Transfer switches, Right angle pointing of the meter head. .......:?
 
In this case, the meter extender includes a compartment for a 240->12VDC power supply, so the tapped "output" is Class 2, used to power fiber-to-the home equipment on the side of the house (owned by the utility). It's got suitably rated fusing and isolation (per UL 2745), designed for the application.
 
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