Generator Cable Question

[WCEI]

Generator cable for residential home standby generators is available with 3 #3 awg copper and 6-#16 awg copper control wires.

When the generator is not running, 3 control conductors are energized with AC current, plus a neutral, and there is 12 volt DC on two other conductors.

When the generator is running the two #3s are energized, plus the neutral, and other than briefly at start up, only one #16 is energized.

The 26 kw generator has a 110 amp main breaker.

Considering all factors, is this generator cable legal to use with a 26 kw unit?

 

[augie47]

That issue came up a while back in our area and the controversy arose as to whether 310.15(B)(7) was applicable and our AHJ ruled it was not and a #3 was not sufficient on a 110 amp OCP device. On the other hand, I havr seen it allowed. Possibly a AHJ call for your area,

 

[WCEI]

That issue came up a while back in our area and the controversy arose as to whether 310.15(B)(7) was applicable and our AHJ ruled it was not and a #3 was not sufficient on a 110 amp OCP device. On the other hand, I havr seen it allowed. Possibly a AHJ call for your area,

Thank you, I’m curious if this is the predominant situation, or other AHJ’s see if differently. One other hiccup is that I’m told the cable is UL listed for 22 and 24 kw generators. I’m not certain that this is accurate. I’m trying to find out who the local rep is for the brand we use. Hopefully they will have some information, good or bad, to put this to rest once and for all.

 

[don_resqcapt19]

Does the generator supply 100% of the dwelling unit loads?

 

[WCEI]

Does the generator supply 100% of the dwelling unit loads?

100% of what has not been automatically load shed.

 

[kwired]

100% of what has not been automatically load shed.

Then that is not 100% of the dwelling unit load, technically. In theory this genset should be able to continuously supply 110 amps, and not shed any loads if current never goes above that level.

 

[WCEI]

Then that is not 100% of the dwelling unit load, technically. In theory this genset should be able to continuously supply 110 amps, and not shed any loads if current never goes above that level.

But, that really doesn’t help answer my question, I don’t believe? Unless I’m missing the point?

 

[augie47]

310.15(B)(7) allows for a reduced size conductor when it is a feeder or service conductor supplying the "entire load associated with the dwelling".
Your generator is likely supplying selected loads thus does not have the load diversity of a "whole house" feeder and the conductor must be protected at it's ampacity of 100 amps so the 110 amp breakers is oversized.

 

[suemarkp]

They still need to fix that section and define the minimum requirements fora dwelling. You could have two houses A and B that are both the same except B has a gas water heater and gas range. If you chose to load shed the water heater and range in house A, it is electrically the same as house B, except house B is allowed to use the "entire dwelling" discount and house A is not.

Same could happen with two identical houses except one with an AC unit and one without. Load shedding the AC unit should not disqualify that house from the entire dwelling discount. Another case would be a dwelling within a dwelling (e.g. mother in law space). A feeder to that MIL space should be allowed to use the discount if it has the minimum dwelling requirements of a kitchen, 1 bedroom, and 1 bathroom.

 

[LarryFine]

It sounds like you guys are saying that a generator feeder that supplies a panel with shed loads must be larger than one feeding unshed loads (with the same total connected load).

In my opinion, a service or feeder that is supplying everything that is being supplied qualifies as feeding the entire load.

However, I do agree that #3cu is not large enough for this 110a breaker, as there are no service conductors for the feeder to not be required to be larger than.

I hope I haven't contradicted myself here.

 

[WCEI]

It sounds like you guys are saying that a generator feeder that supplies a panel with shed loads must be larger than one feeding unshed loads (with the same total connected load).

In my opinion, a service or feeder that is supplying everything that is being supplied qualifies as feeding the entire load.

However, I do agree that #3cu is not large enough for this 110a breaker, as there are no service conductors for the feeder to not be required to be larger than.

I hope I haven't contradicted myself here.

IF you could use the #3 at the 90c rating, and did not have to derate because of the number# of conductors, then it’s good for 110 amps.

Question is since it’s a cable, more like Tray cable than Romex, can you use it at 90c? Are the terminals all 90c rated, (which I believe they would be), is there a UL listing on the cable that says to use the conductors at a certain x-rating, and do you have to derate for the number of conductors, (which I would argue that no, you do not), can you use it on the 110 amp breaker? A lot of questions and “ifs”? So can it be used in this application? As an electrician I would say, sure you can. As an inspector I would say no, unless you can prove to me that it satisfy’s all my concerns.

 

[WCEI]

They still need to fix that section and define the minimum requirements fora dwelling. You could have two houses A and B that are both the same except B has a gas water heater and gas range. If you chose to load shed the water heater and range in house A, it is electrically the same as house B, except house B is allowed to use the "entire dwelling" discount and house A is not.

Same could happen with two identical houses except one with an AC unit and one without. Load shedding the AC unit should not disqualify that house from the entire dwelling discount. Another case would be a dwelling within a dwelling (e.g. mother in law space). A feeder to that MIL space should be allowed to use the discount if it has the minimum dwelling requirements of a kitchen, 1 bedroom, and 1 bathroom.

Very good points sir.

 

[augie47]

As to the 90°:
"Are the terminals all 90c rated, (which I believe they would be)"
The terminal (lug) might well be 90° rated but the device to which it is attached, such as a breaker, most likely is not and it's that device that 110.14 addresses. As a general rule you can assume the 90° rating is useful for ambient and fill derating purposes only.
In addition, 336.80 dictates the ampacity for TC.

As I noted in Post #2, this issue seemingly is not a black n white one and debate can continue but the answer lies with your AHJ. Some accept, some don't.

 

[jim dungar]

IF you could use the #3 at the 90c rating, and did not have to derate because of the number# of conductors, then it’s good for 110 amps.

Question is since it’s a cable, more like Tray cable than Romex, can you use it at 90c? Are the terminals all 90c rated, (which I believe they would be)....

I know of no UL listed breaker or fusible switch with terminations rated at 90°C.
Even 100% rated devices which may require 90°C insulated conductors are still only rated with 75°C terminations

 

[WCEI]

As to the 90°:
"Are the terminals all 90c rated, (which I believe they would be)"
The terminal (lug) might well be 90° rated but the device to which it is attached, such as a breaker, most likely is not and it's that device that 110.14 addresses. As a general rule you can assume the 90° rating is useful for ambient and fill derating purposes only.
In addition, 336.80 dictates the ampacity for TC.

As I noted in Post #2, this issue seemingly is not a black n white one and debate can continue but the answer lies with your AHJ. Some accept, some don't.

I’ll check to be sure, but I believe that the terminals in Generac generators and ATS’s are 90c rated.
336.8 doesn’t seem to answer my question. Can the conductors in Tray cable be used at their full rating, (assuming that it is 90c)? And, is Gen cable actually tray cable?

I’m working to validate what I think is the case.

 

[WCEI]

I know of no UL listed breaker or fusible switch with terminations rated at 90°C.
Even 100% rated devices which may require 90°C insulated conductors are still only rated with 75°C terminations

Ummmm??? I’m not sure I agree.

 

[augie47]

 

[kwired]

Ummmm??? I’m not sure I agree.

Please find us an example. As Jim mentioned you may find the lug itself on a switch or breaker might say 90C but the switch or breaker assembly itself is still only rated 75C and you simply just won't find any assembly rated 90C especially in the under 1000 volt category. Not saying it is impossible but would be pretty rare. Stand alone terminal bars, lugs and similar might be easy to find in 90C rating. Attach them to another device and that device is likely only 75C and will be a limiting factor.

 

[don_resqcapt19]

There are some 100% rated breakers for under 1000 volts, but they are not common and require a larger than normal size enclosure as the only reason for thee 80% limit is heat. The smallest I saw was 125 amps. They require the use of 90°C conductors used at the 75°C ampacity. The 125 amp 3 pole K frame 100% rated breaker has a minimum enclosure size of 24" x 15" x 6" and you can only have that one breaker in the enclosure.
Eaton 100% rated breaker