nec 2017 inverter output ampacity with circuit breaker

[jjavier]

Hi

I have a doubt in nec 2017


It seems that in the nec 2017 if you have a adjustable electronic circuit breaker, you don´t have to multiply *1,25 the amperage in the ouput of the inverter. Is it true?

Regards

 

[pv_n00b]

My take on this is that electronic CBs are not thermally activated devices. The concern with continuous current causing heating that lowers the trip point is then not an issue. They are probably trying to say that an electronic CB is treated like a 100% rated CB, but it is poorly written. There’s nothing in the ROP or ROC about this change. I’m going to ask someone on the CMP and see if I can find out more.

 

[jaggedben]

This seems to have been put it so that 690 wouldn't be construed to conflict with 240.6

 

[310 BLAZE IT]

My take on this is that electronic CBs are not thermally activated devices. The concern with continuous current causing heating that lowers the trip point is then not an issue. They are probably trying to say that an electronic CB is treated like a 100% rated CB, but it is poorly written. There’s nothing in the ROP or ROC about this change. I’m going to ask someone on the CMP and see if I can find out more.

I think the wording difference highlights that the 100 percent cb is at the cb rating but adjustable trip electronic cb is at that adjusted rating.

Do you agree? That is my interpretation of the 100 percent breaker exception, but I'd like to hear other opinions.

Electronic trip can still be thermal magnetic which I thought was also not able thermally compensated and needs to increase for the ambient temperature above 40c.

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[pv_n00b]

I’ve asked 2 people on CMP 4 and both said the wording was difficult. Neither of them would tell me how to apply it to size a conductor. Both said it was meant to refer to the setting of an adjustable OCPD and that the conductor has to be protected by that rating. So this will be a target for revision in 2020.

Here’s how I would interpret it.

NEC 240.6 describes when the adjustment of an adjustable OCPD can be considered the rating and when it cannot. The adjustment has to have restricted access to be considered the rating, otherwise the rating is the maximum value it could be adjusted to.

How does this effect 690.8(B)? I don’t see how it can. Once you have adjusted an adjustable OCPD you treat it just like any other OCPD. The conductor has to be rated to carry the PV current from 690.8(B)(1) or (2) and has to be protected by the OCPD, just as always. Basically I would just ignore the reference to adjustable OCPD, other than to be reminded that they can be used as defined in 240.6.

NEC 690.9(B) also adds something for adjustable OCPDs. It lists the 3 way to select an OCPD rating as 80%, 100%, and I don’t know because 690.9(B)(3) does not lead to a rating. So I will be ignoring 690.9(B)(3), and if I use an adjustable OCPD I will set it for 80% or 100% depending if it is fully rated.

I would really like to hear any alternative interpretations. I’m just taking my best shot here. And ignore what I said earlier in this thread.

 

[jaggedben]

To repeat...

This seems to have been put it so that 690 wouldn't be construed to conflict with 240.6

I think you basically hit the nail on the head in your last post. The practical consequence, it seems to me, is that on 'behind the fence' projects where access is restricted to solar qualified personnel, the settings of adjustable trip devices can be used for sizing conductors. This could be important for the confidence of combiner manufacturers to know how their products can be used. Residential projects and commercial projects without restricted access won't get to take advantage.

 

[pv_n00b]

They really should have an option to delete posts

 

[pv_n00b]

I think you basically hit the nail on the head in your last post. The practical consequence, it seems to me, is that on 'behind the fence' projects where access is restricted to solar qualified personnel, the settings of adjustable trip devices can be used for sizing conductors. This could be important for the confidence of combiner manufacturers to know how their products can be used. Residential projects and commercial projects without restricted access won't get to take advantage.

But the “restricted access” in 240.6 is not that strict:

(1) Removable and sealable covers over the adjusting means​

(2) Bolted equipment enclosure doors​

(3) Locked doors accessible only to qualified personnel​

This could easily be provided for in C&I environments, particularly #1.

 

[ggunn]

They really should have an option to delete posts

I'm pretty sure that if you PM a mod they can do it for you. If it's one of your own, of course.

 

[GoldDigger]

I'm pretty sure that if you PM a mod they can do it for you. If it's one of your own, of course.

Yes.

 

[jjavier]

Thanks!

Thanks!

In our design we have fuses (cheaper)... so we can use this articule of the nec ... and seems not to be completly clear

Yes.

 

[310 BLAZE IT]

In our design we have fuses (cheaper)... so we can use this articule of the nec ... and seems not to be completly clear

Fuses are difficult to get manufacturer listed to be 100 percent rated with the assembly in order to use this code section. They wouldn't fall under the adjustable breaker section either.

I will have to read through 260.4 again to see how the wording applies

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[jjavier]

fuses

fuses

Sorry , I meant can´t use with fuses.

Fuses are difficult to get manufacturer listed to be 100 percent rated with the assembly in order to use this code section. They wouldn't fall under the adjustable breaker section either.

I will have to read through 260.4 again to see how the wording applies

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[pv_n00b]

Yes.

That’s great but it’s better if the user could delete them. This is only one of two sites that I know of that do not allow a user to delete their own post. I’ve seen other users just edit a post to read “deleted” and it’s easier to do that than to PM a moderator, and nothing is gained over allowing the user to delete the post.

 

[GoldDigger]

That’s great but it’s better if the user could delete them. This is only one of two sites that I know of that do not allow a user to delete their own post. I’ve seen other users just edit a post to read “deleted” and it’s easier to do that than to PM a moderator, and nothing is gained over allowing the user to delete the post.

The problem I see is that once the Edit time window has expired, it would no longer be possible to delete anyway.

mobile

 

[pv_n00b]

The problem I see is that once the Edit time window has expired, it would no longer be possible to delete anyway.

mobile

All depends on how they set it up. Maybe edit has a time limit but delete does not.