Terminal blocks for service wires

[Mr. Serious]

Are there terminal blocks that are rated for use with un-fused service conductors? I recall seeing a somewhat-new code provision requiring that such blocks be specifically rated for it, when used in this way. But I can't remember the exact wording or where in the code to find it.

As a new contractor last year, I built a service with two parallel 350MCM aluminum conductors per phase through the underground conduit, which transitioned to two 250MCM copper conductors via terminal blocks mounted in a box below the main panel. NSI ALP2P2 connector bloks. The reason was to save money on the 130-foot long underground wires while keeping the main wires into the panel small enough to fit into its lugs. But later I thought it maybe would have been a lot easier to order custom lugs for the panel.

So, now I'm working on another large new service. Service equipment for these things sometimes can't be ordered on any reasonable time frame. So, we're working with the only panel that was available. The panel comes with lugs rated for (2) parallel runs of up to 600MCM, which would require copper to get the full 800 amps, but the customer wants to mainly use aluminum to save money, the power company diagrams show a splice in the main wires inside the CT cabinet anyway. This time, some way is required to splice between (4) or (6) smaller aluminum wires to (2) larger copper ones for each phase. I was looking at the NPDB-14-750-1, but I want to do things right this time, and I think all connector blocks like this require a fuse ahead of the block. So, what do I use for connectors for unfused service wires? Polaris lugs?

Or, is it more prudent to check with the power company to see if the splice in the CT cabinet is really required, and if not, see if different main lugs can be ordered for the panel?

 

[petersonra]

Are wires in the CT cabinet actually covered by the national electrical code?

My understanding is that the mechanical terminals like these are only rated for 10,000 Amps of short circuit current while crimp on connectors are considered part of the wire by UL and thus the available short circuit current does not matter much. Or so I have been told.

I took a look at the catalog page for this particular block and it says the default short circuit current rating is 10K. Not only that it is not listed it is only recognized.

 

[electrofelon]

There is such a requirement, new in the 2020 if I remember, that says something about connectors or terminal blocks on the line side of the service be listed for such use. I don't recall the wording, but I seem to remember there is a differentiation between terminal blocks and not terminal blocks. Hopefully someone can fill in the gaps.

Can't you just transition to the conductors you need on the load side of the CT mounting base without making an additional splice?

 

[petersonra]

The other block you mentioned. Appears to be listed but is only listed for higher short circuit currents up to 110 amps it fused with class j fuses. I don't think that's going to help you a whole lot.

 

[cadpoint]

Your regional/State POCO usually publishes installation guide lines for what they expect. I have heard twice (regionally) in the field where the Poco's have or like to have a lineal run closer to their source drop so the owner is paying for the run of power and usually owns the distribution cabinet but is govern by POCO.
I don't think like an Engineer so I have no discussion points in respects to "Amps of short circuit current" but thanks for bringing it up
- Mr. Petersonra.
I found the OP's linked comparison Odd in respects to the informational presentation was so different - page to page, If one uses the second link and goes to NPDB Cross Reference in Documents, this presents a broader manufactured cross reference guide.

 

[Mr. Serious]

This is the first service I have built with a CT cabinet, so there are some things I may not be aware of. Here is one:

Can't you just transition to the conductors you need on the load side of the CT mounting base without making an additional splice?

The CT's have a mounting base with terminals/lugs? I was envisioning something with just a ring to run the main wires through. So, I need to check with the power company to get details about their CTs.

And the second one:

Are wires in the CT cabinet actually covered by the national electrical code?

Good question!

Basically, I need to check with the power company and get details of what a good installation actually looks like before finalizing a design and ordering materials for this. I have seen their main requirements document with figures for each type of service, but it doesn't give any detail on what the CTs actually look like.

 

[tom baker]

Our poco has an excellent customer handbook, it’s well coordinated with the NEC

 

[brantmacga]

What gear are you using? When I’m ordering panels, part of the review process involves checking all lug configurations against the conductors we’ll be using.

I use a lot of square D breakers and you can get P-frames with triple 350-600 lugs. You have to specify that in the order though. Bought separately they’re $600 per set of 3.

It’s likely whatever you’re using has a configuration available that will accept your conductors.


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[electrofelon]

This is the first service I have built with a CT cabinet, so there are some things I may not be aware of. Here is one:

The CT's have a mounting base with terminals/lugs? I was envisioning something with just a ring to run the main wires through. So, I need to check with the power company to get details about their CTs.

Yes. Typically you will buy a CT cabinet which is the cabinet itself, and also a CT mounting base which has lugs (or just studs if you want it that way for crimp on terminals) and will take bar type CT's that bolt on.

Example: https://hoffman.nvent.com/en-us/products/encctmb8001

 

[electrofelon]

Are wires in the CT cabinet actually covered by the national electrical code?

Yes of course. Typically the CT cabinet and meter enclosure are supplied, owned and installed by the customer. The power company will still own the CT's themselves, just like they would a self-contained meter. Of course there are probably some cases where the CT cabinet is on the line side of the service point and thus owned by the power company.

 

[Mr. Serious]

I think I am not working with bar-type CTs. I have checked with the power company representative. I just need to finish drawing up these plans and run it by everyone and make sure it's all good, then order the parts and install it.

If the code change that requires terminal blocks to be rated for use on the line side service wires didn't happen until the 2020 code, then I guess I can still use these blocks or something very similar. We're on 2017 code now in OK.

 

[don_resqcapt19]

....

The CT's have a mounting base with terminals/lugs? I was envisioning something with just a ring to run the main wires through. So, I need to check with the power company to get details about their CTs.

....

I have never seen donut type CTs used by a utility for their revenue meter.

 

[brantmacga]

I have never seen donut type CTs used by a utility for their revenue meter.

I'm in the southeast, and window CT's are the primary means of metering by the dozens of utilities I work with, and I hate them. I did one job a couple of years ago, 600A single-phase, and the utility provided me with bar-type to install. So much easier.

 

[paulengr]

What gear are you using? When I’m ordering panels, part of the review process involves checking all lug configurations against the conductors we’ll be using.

I use a lot of square D breakers and you can get P-frames with triple 350-600 lugs. You have to specify that in the order though. Bought separately they’re $600 per set of 3.

It’s likely whatever you’re using has a configuration available that will accept your conductors.


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Square D has an amazing variety of lug configurations but they are the exception, not the rule. Some others offer lugs or bus bars. That’s it.

 

[electrofelon]

I'm in the southeast, and window CT's are the primary means of metering by the dozens of utilities I work with, and I hate them. I did one job a couple of years ago, 600A single-phase, and the utility provided me with bar-type to install. So much easier.

So how does that work? Does the POCO provide you with the CT's and you install them over the conductors? Do need to leave a splice or terminal block?

 

[brantmacga]

So how does that work? Does the POCO provide you with the CT's and you install them over the conductors? Do need to leave a splice or terminal block?

Utilities always provided them. We get them before the secondary pull.

I’d say 99% of the utilities I work with do not allow and splicing/terminal blocks inside the CT cabinet .


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[electrofelon]

Utilities always provided them. We get them before the secondary pull.

I’d say 99% of the utilities I work with do not allow and splicing/terminal blocks inside the CT cabinet .


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So you just pull the conductors through a box or cabinet and leave the CTs over the conductors? Interesting. Where do they get the voltage?

 

[brantmacga]

So you just pull the conductors through a box or cabinet and leave the CTs over the conductors? Interesting. Where do they get the voltage?

you mount the CT's to a backboard and pull conductors through the windows.

The utility will tap voltage from the secondary; they usually hook an eye on the end of their conductor and drill a screw through it into our secondary.

 

[LarryFine]

I have also seen them use a small U-bolt to tie a meter voltage lead to a single strand of each wire.

 

[don_resqcapt19]

I'm in the southeast, and window CT's are the primary means of metering by the dozens of utilities I work with, and I hate them. I did one job a couple of years ago, 600A single-phase, and the utility provided me with bar-type to install. So much easier.

That is all they use around here.