Buzzer and bell transformer

[busman]

Apparently I was wrong!

Ron

I missed the grounded secondary also.

Mark

 

[wwhitney]

250.30(A)(4) Exception 3

Thank you! At least for the 2020 NEC, it's 250.30(A)(5) Exception 3.

So that answers the OP's questions (1) and (2): for a voluntarily grounded Class 1, 2, or 3 transformer secondary of at most 1000VA, the GEC may be omitted per the above, and the system bonding jumper can just be sized as 250.30(A)(1) Exception 3, generally just the EGC of the circuit supplying the transformer.

As to question (3) on OCPD, there's nothing directly in Article 240 that lets you omit it, but 240.3 does refer you to Article 725, which can amend Article 240. I expect the allowance is in Article 725 somewhere, although it may only apply to Class 2 and Class 3 sources. Any pointers?

Cheers, Wayne

 

[Besoeker3]

Very much simpler for me - batteries. They have lasted four years so far.

 

[tortuga]

Thank you! At least for the 2020 NEC, it's 250.30(A)(5) Exception 3.

So that answers the OP's questions (1) and (2): for a voluntarily grounded Class 1, 2, or 3 transformer secondary of at most 1000VA, the GEC may be omitted per the above, and the system bonding jumper can just be sized as 250.30(A)(1) Exception 3, generally just the EGC of the circuit supplying the transformer.

As to question (3) on OCPD, there's nothing directly in Article 240 that lets you omit it, but 240.3 does refer you to Article 725, which can amend Article 240. I expect the allowance is in Article 725 somewhere, although it may only apply to Class 2 and Class 3 sources. Any pointers?

Cheers, Wayne

I typically run 18AWG for 24 volt stuff like that see Table 11(A) for Inherently Limited Power Source Overcurrent Protection is Not Required
otherwise for 24 volts a 4A fuse would suffice. Also 240.4(D)(1)

 

[texie]

As others have correctly noted, such as the OP's situation, the secondary of most Class 2 24 volt xformers do not need to be grounded. But it is worth noting that there are many cases where it is required such as HVAC equipment that is supplied at 480 volt, 480 volt pump control panels, etc. In these cases the code requires the 24 volt control secondary to be grounded. This does not necessarily mean they need a GES.

 

[don_resqcapt19]

But 250.20(A) allows it to be a grounded system, and the schematic posted shows a grounded secondary.

250.30(A)(1) Exception 3 then provides relief on the System Bonding Jumper size in this application. Does anything provide relief for a GEC connection for such an installation?

Cheers, Wayne

details details details

250.30(A)(5) Exception 3 addresses the GEC.


However if you leave it an ungrounded system as most are, I don't see anything that says a grounding electrode system and grounding electrode conductor is not required.

 

[tortuga]

However if you leave it an ungrounded system as most are, I don't see anything that says a grounding electrode system and grounding electrode conductor is not required.

I hinted at that in post 17, 251.121 Exception permits a wire type branch circuit equipment ground to be the GEC.

 

[don_resqcapt19]

I hinted at that in post 17, 251.121 Exception permits a wire type branch circuit equipment ground to be the GEC.

but does not change the minimum permitted size of the GEC..EGC would have to be 8 AWG and follow all of the other rules for GECs.

 

[wwhitney]

However if you leave it an ungrounded system as most are, I don't see anything that says a grounding electrode system and grounding electrode conductor is not required.

For ungrounded SDSs, 250.30(B)(1) says "A grounding electrode conductor . . . shall be used . . . as specified in 250.30(A)(5) or (6), as applicable." And 230.30(A)(5) has Exception 3 for "a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes." So the Exception applies to ungrounded SDSs, by direct reference.

Cheers, Wayne

 

[texie]

details details details

250.30(A)(5) Exception 3 addresses the GEC.


However if you leave it an ungrounded system as most are, I don't see anything that says a grounding electrode system and grounding electrode conductor is not required.

Well gee, you have raised an interesting question for sure. But yet we know that the typical ungrounded 24 volt control secondary never has a GES. Is this an oversight in the code that has never been caught? It seems odd that it is clear for grounded control circuits derived from an xformer but not for the more typical ungrounded control circuit xformer. Gonna need some research for sure.

 

[wwhitney]

Gonna need some research for sure.

See the previous post. : - )

Cheers, Wayne

 

[texie]

See the previous post. : - )

Cheers, Wayne

Wayne, I did see it, but I'm try to make the leap that you suggest. Help me here.

 

[letgomywago]

Well gee, you have raised an interesting question for sure. But yet we know that the typical ungrounded 24 volt control secondary never has a GES. Is this an oversight in the code that has never been caught? It seems odd that it is clear for grounded control circuits derived from an xformer but not for the more typical ungrounded control circuit xformer. Gonna need some research for sure.

I think it has to do with it being a class 1,2, or 3 transformer but I'm not sure.

 

[wwhitney]

Wayne, I did see it, but I'm try to make the leap that you suggest. Help me here.

To oversimplify, 250.30(B)(1) says "do it like 250.30(A)(5) or (6)." And 250.30(A)(5) has the exception we are expecting.

Cheers, Wayne

 

[Besoeker3]

Very much simpler for me - batteries. They have lasted four years so far.

And no ground required - simple innit......................

 

[ggunn]

I don't hear no buzzers and bells. I play by sense of smell.

 

[LarryFine]

I don't hear no buzzers and bells. I play by sense of smell.

There's got to be a twist!

 

[rc/retired]

Are you guys pinball wizards?

 

[texie]

To oversimplify, 250.30(B)(1) says "do it like 250.30(A)(5) or (6)." And 250.30(A)(5) has the exception we are expecting.

Cheers, Wayne

Well, it seems you may be correct. Kind of convoluted but I guess this is what gives us the allowance for no GES in the situation we are discussing.