Line side tap - enough space in the switchboard?

filliamHmuffman

New member
Location
Fresno, CA
Help out a dumb engineer...

We're planning a line side tap into existing gear for a commercial PV installation. The PV aggregates into a 1200A switchboard which will then go in as a line side tap into the existing main switchboard (2000A bus, 1600A main). POCO is OK with the arrangement as long as we don't break their seals and maintain the UL listing of the gear. So my questions are:

- What does that line side tap actually look like? Seems like an awful lot of tapping going on a pretty small area.
- The switchboard is a top mount meter with a bottom mount main. Is it at all realistic to be able to come in from the top without breaking any POCO seals?
- Is there any chance of getting the manufacturer to sign a document that the UL listing will not be compromised for 25 year old gear?
- Is there a better way to go about this without breaking the bank?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Help out a dumb engineer...

We're planning a line side tap into existing gear for a commercial PV installation. The PV aggregates into a 1200A switchboard which will then go in as a line side tap into the existing main switchboard (2000A bus, 1600A main). POCO is OK with the arrangement as long as we don't break their seals and maintain the UL listing of the gear. So my questions are:

- What does that line side tap actually look like? Seems like an awful lot of tapping going on a pretty small area.
- The switchboard is a top mount meter with a bottom mount main. Is it at all realistic to be able to come in from the top without breaking any POCO seals?
- Is there any chance of getting the manufacturer to sign a document that the UL listing will not be compromised for 25 year old gear?
- Is there a better way to go about this without breaking the bank?
I have done line side taps by landing my conductors on lugs installed on unused perforations in the busbars on the line side of switchgear main breakers. I have contacted switchgear manufacturers and been told verbally that they have no problem with doing that but getting it in writing has been more difficult. They seemed surprised at the question, their attitude seemed to be largely "of course you can do that; what makes you think you can't?"

BTW, your fused disco from the PV must be within 10' from the tap as the conductor flies.
 

jaggedben

Senior Member
- What does that line side tap actually look like? Seems like an awful lot of tapping going on a pretty small area.
Pretty much the answer is based on the specific case. Usually you are looking for a place where busbars are bolted together and you can add lugs to those existing bolts. Barring that, you might have to drill holes in busbars to accomplish the same thing. Anything you do has to be okay per the switchgear manufacturer, or else field listed (see below.)

Be careful of running the conductors for the PV through the load side sections of the switchgear, that may not be kosher per manufacturer and/or AHJ.

- The switchboard is a top mount meter with a bottom mount main. Is it at all realistic to be able to come in from the top without breaking any POCO seals?
Based on my admittedly very limited experience with this size switch gear ... Probably not.

- Is there any chance of getting the manufacturer to sign a document that the UL listing will not be compromised for 25 year old gear?
The only way to find out is to ask them.

- Is there a better way to go about this without breaking the bank?
A better way than a line side tap? Doesn't sound like it from your numbers.

If the manufacturer doesn't green light your plan, yu can pay UL to send a representative out and 'field list' whatever you do. This will cost several thousand but that's much less than replacing 2000A switchgear. You would probably need to pay them for two or three visits: one pre-install to agree that what you propose is okay in theory, and a post-install visit to confirm that what you did conformed to the plan. Make the POCO and AHJ are cool with having the install field listed.
 
Just to add to what others have said: In my experience, the bolt patterns of most bus bars in switchboards conform to NEMA standard bolt patterns, thus one can usually find a lug, such as the ilsco PB series for example, that fits right on, perhaps with longer bolts. You also may luck out and find lugs already there. The last 8 350KW-ish systems we did ALL had available lugs in the gear.

POCO is OK with the arrangement as long as we don't break their seals
This is a bit odd. Think about it - almost every electrical system has customer terminations in a sealed meter or CT cabinet. Why should they care that your connections land in the metering section of the switchboard (on the correct side of the CT's!)?
 
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