Power Distribution Blocks/Taps

[J2H]

A recent off-air event resulted in the discovery of overheated line side conductors at a 60 amp transmitter disconnect, presumably due to insufficient torque.

Under investigation, I found that the#4 feed to the disconnect comes from a power distribution block, where it is double-tapped with a 3/0 1 per phase.

The other side of the distribution block is a 250 run as parallel conductors from an ATS.

One set of 250s feeds the the aforementioned disconnect, the other feeds a 200 amp disconnect with 3/0 fed through another set of blocks.

Would it be compliant to come off the first set of blocks with a set of 250s and tap to the panel and 60 amp disconnect with a Polaris tap for example?

Other possible solutions would be to replace the blocks with blocks that accommodate more wires, but it looks blocks to accommodate these sizes on the load side are limited.

The other option, which I don’t really think is a great one would be to replace the disconnect with a breaker, but that is probably the simplest and lowest cost.

 

[petersonra]

A recent off-air event resulted in the discovery of overheated line side conductors at a 60 amp transmitter disconnect, presumably due to insufficient torque.

Excessive torque is maybe worse. It needs to be torqued to the manufacturers instructions.

Under investigation, I found that the#4 feed to the disconnect comes from a power distribution block, where it is double-tapped with a 3/0 1 per phase.

I don't know what you mean by double tapped. if you mean there is a hole with a #4 and 3/0 in the same hole, it is probably not code.

The other side of the distribution block is a 250 run as parallel conductors from an ATS.

One set of 250s feeds the the aforementioned disconnect, the other feeds a 200 amp disconnect with 3/0 fed through another set of blocks.

Would it be compliant to come off the first set of blocks with a set of 250s and tap to the panel and 60 amp disconnect with a Polaris tap for example?

Other possible solutions would be to replace the blocks with blocks that accommodate more wires, but it looks blocks to accommodate these sizes on the load side are limited.

The other option, which I don’t really think is a great one would be to replace the disconnect with a breaker, but that is probably the simplest and lowest cost.

maybe a sketch is in order. its hard to follow what it is you are trying to tell us.

 

[J2H]

Excessive torque is maybe worse. It needs to be torqued to the manufacturers instructions.


I don't know what you mean by double tapped. if you mean there is a hole with a #4 and 3/0 in the same hole, it is probably not code.




maybe a sketch is in order. its hard to follow what it is you are trying to tell us.

Yes, there is a 3/0 and #4 in the same hole.

I can post a sketch, but here is a photo of the distribution blocks.

Right side is feed from an ATS with 2 250s per phase.

The upper blocks on the left feed a 200 amp disconnect with 3/0.

The lower blocks feed a 60 amp disconnect and 200 amp load center.

 

[petersonra]

This looks more like a splice block to me then a distribution block.

 

[J2H]

Thank you for your thoughts particularly about the over torquing.

In my mind continuing through with a 250 to an appropriate multi terminal block, and then attaching the 3/0 and the #4 to that block would compliant as the first connection is a splice and not a tap.

 

[petersonra]

Thank you for your thoughts particularly about the over torquing.

In my mind continuing through with a 250 to an appropriate multi terminal block, and then attaching the 3/0 and the #4 to that block would compliant as the first connection is a splice and not a tap.

Probably. Depends on what is upstream and maybe how far you plan to run the tap conductors. There are several scenarios where the existing setup does not meet code beyond putting two wires on one terminal.

Personally, I would be inclined to leave the 250 and 3/0 where it is and move the #4 to some kind of Polaris style connector on the 250. Or even a vampire (idc) connector. Less work.

 

[J2H]

Thanks for your reply. Speaking of the existing setup not meeting code, it occurred to me that since the ATS is fed from a 400 Amp disconnect, the current arrangement of the 250s makes them tap connectors, so unless both the blocks and the ATS terminals are 90 degree rated which is doubtful, this is a violation.

Here is a quick sketch.

 

[petersonra]

Thanks for your reply. Speaking of the existing setup not meeting code, it occurred to me that since the ATS is fed from a 400 Amp disconnect, the current arrangement of the 250s makes them tap connectors, so unless both the blocks and the ATS terminals are 90 degree rated which is doubtful, this is a violation.

Here is a quick sketch.

Unfortunately when you start trying to fix some of these things, other stuff comes to light. It is why people sometimes see very narrowly.

 

[J2H]

Yep, that is very true. While not ideal, it’s seeming like the most straightforward solution in this case would be to eliminate the 60 amp disconnect and replace that with a 3 pole breaker in the load center.

The better, and more involved option would be to use something a like a Polaris connector or replacement terminal block to parallel the 250s and then tap to the load side 3/0s and #4.

 

[Elect117]

#4 is too small for a 25' tap rule. You will need something with an ampacity over 120A. You will need #1 or 1/0 Cu depending on the temperature terminal ratings / breaker rating / panel rating.

Also, on the first picture, I can't tell but it looks like the two phases that burnt were aluminum and the other was copper. Aluminum conductors have a lower rating.

 

[J2H]

That’s a good point. Fortunately in this case nothing is over 25 ft.

My current plan is to go from the blocks to a 5 port Polaris tap.

The 250s can be recombined, and the #4 and 3/0s connected as taps.

I realize that the blocks can be completely eliminated with the Polaris taps, but I don’t see any harm in leaving them, and it makes the work a little simpler.

This building is similar to what cell phone companies used and appears to have been prewired. Perhaps the intent of the blocks was to permit on site connection of 2 200 amp panels.

I also noticed the strange oxidation on the two burnt phases. It’s out of the frame of the photo, but beneath the oxidized area, the conductors look like copper. I’ll get a closer look tonight, but I’m considering the possibility of copper clad aluminum conductors.