Tap Question

[iwire]

I think that IPC's are designed to establish connections without shutting down. Solar Pro (the magazine) thinks so, too.[/B]

There is virtually no case where hot work rules would allow this.

 

[ggunn]

There is virtually no case where hot work rules would allow this.

I know for a fact that it (installing IPC's on the line side without shutting down the service) is a common practice in PV installations.

 

[Smart $]

I know for a fact that it (installing IPC's on the line side without shutting down the service) is a common practice in PV installations.

Being a common practice does not make it a safe practice.

On top of that, they are probably not even donning the proper PPE for doing energized work. :rant::rant::rant:

 

[SolarPro]

Yeah, that's a classic SolarPro article, published in 2009. I'm hoping to revisit the topic in 2017, in part because the Code requirements, not to mention the Code references, have changed so much.

It's also fair to say that the article doesn't represent best practices for electrical safety. If you study NFPA 70E, Handbook for Electrical Safety in the Workplace, I think you'll find that there's really no situation where an electrician should be interconnecting to an energized service.

Do people do it? Probably so. But it's an accident waiting to happen.

Similarly, there's also no excuse for sending crews up onto a roof without fall protection, although this also seems to be a common practice in the PV industry. Hopefully, everyone at your company keeps making it home safe. However, I'm pretty confident that if there ever is an accident, OSHA will find some institutional deficiencies with your safety program.

Take it from mom: It's always fun until someone gets hurt.

 

[csoc64]

No. You are asking for trouble by doing this. Anytime there are parallel conductors, you have to preserve the symmetry as much as possible.

I made a graphic illustrating the problem with only tapping onto one of the parallel conductors. Problem: calculate the current in R1, R1', and R2, given the resistances and the voltages V1, V2, and the current IPV. This represents a long feeder that is made up of parallel 250 kcmils with a 2% voltage drop across the source feeder. The PV is tapped very close to the load on set #1 of that feeder.

Do you exceed the ampacity of the 250 kcmil wire, in any portion of it?
View attachment 15420

The proper way to do this, is with a 5-terminal insulated tap connector, that has an input and output port for both wires in the existing parallel set, and then a 5th port for the PV. Or any other method that allows you to connect onto both existing conductors. A nice way to do this, is when you have an unused lug position on the existing breaker.

How about a 3 terminal insulated tap connector with an input for the pv circuit and two outputs to feed the parallel set with IP connectors?

 

[Carultch]

How about a 3 terminal insulated tap connector with an input for the pv circuit and two outputs to feed the parallel set with IP connectors?

The issue there, is that you would be terminating your "tap conductors" in to something other than an overcurrent protection device. If 240.21(B) applies in the application, this would not be permitted. It would be making a tap from a tap.

 

[Smart $]

...
The proper way to do this, is with a 5-terminal insulated tap connector, that has an input and output port for both wires in the existing parallel set, and then a 5th port for the PV. Or any other method that allows you to connect onto both existing conductors. A nice way to do this, is when you have an unused lug position on the existing breaker.

How about a 3 terminal insulated tap connector with an input for the pv circuit and two outputs to feed the parallel set with IP connectors?

The issue there, is that you would be terminating your "tap conductors" in to something other than an overcurrent protection device. If 240.21(B) applies in the application, this would not be permitted. It would be making a tap from a tap.

I believe his question is regarding the use of a 3-conductor IPC, which electrically is no different than a "5-terminal insulated tap connector" that requires cutting the two paralleled conductors.

 

[pv_n00b]

I don't think there is a great way to connect to parallel conductors, better to avoid it when possible. Messing with them is like tickling the sword juggler, maybe nothing happens, maybe you get a sword in the head. :jawdrop:

The least problematic way think would be to bring the parallel conductors together using something like an insulated tap connector that connects the conductors, then back feeding that point, and paralleling again. Then you have essentially created two series parallel circuits that hopefully are balanced. The down side is that any terminations in the circuit could go bad and become high resistance compared to the other parallel path and overload the parallel conductor.

Remember that the individual parallel conductors are not rated to carry the full current and are not protected by the OCPD. The whole thing is protected by virtue of proper design and installation.