Line side tap

[bob52]

I am working on a 1 megawatt system that involves a line side tap to a fused disc. switch. My question is should the tap conductors be run to the line or load side of the fused disc.?

 

[Smart $]

I am working on a 1 megawatt system that involves a line side tap to a fused disc. switch. My question is should the tap conductors be run to the line or load side of the fused disc.?

Line side always goes toward the utility source.
Load side always goes away from the utility source.

 

[Carultch]

I am working on a 1 megawatt system that involves a line side tap to a fused disc. switch. My question is should the tap conductors be run to the line or load side of the fused disc.?

Another rule of thumb, is that the hinge of the disconnect blade should point toward the inverter. This way, the side that remains energized when the disconnect is open, is the side connected to the line side terminals. The AC side of the inverter will de-energize on loss of utility power. The DC side will eventually de-energize when the capacitors bleed down, in contrast from the PV side which remains energized as long as there is sunlight.

 

[SolarPro]

Another rule of thumb, is that the hinge of the disconnect blade should point toward the inverter. This way, the side that remains energized when the disconnect is open, is the side connected to the line side terminals. The AC side of the inverter will de-energize on loss of utility power. The DC side will eventually de-energize when the capacitors bleed down, in contrast from the PV side which remains energized as long as there is sunlight.

Great rule of thumb.

 

[Smart $]

Another rule of thumb, is that the hinge of the disconnect blade should point toward the inverter. This way, the side that remains energized when the disconnect is open, is the side connected to the line side terminals. The AC side of the inverter will de-energize on loss of utility power. The DC side will eventually de-energize when the capacitors bleed down, in contrast from the PV side which remains energized as long as there is sunlight.

Great rule of thumb.

It's actually the same rule of thumb that I posted, only worded differently.

 

[electrofelon]

Line side always goes toward the utility source.
Load side always goes away from the utility source.

I am reading the question a little differently - not really sure what the op is asking. Is the switch in question the normal/existing service diconnect? If so, it wouldn't be a line side connection if you connect to the load side.....

 

[electrofelon]

Ok reread, I get it. That's a common question. I was going "the other direction".

 

[ggunn]

I remember having a... discussion with someone (might have been in here) who for a while insisted that the inverter goes on the line side of the PV AC disco. I told him something to the effect that when it was time to put the fuses in he'd better have his life insurance paid up.

 

[Smart $]

I am reading the question a little differently - not really sure what the op is asking. Is the switch in question the normal/existing service diconnect? If so, it wouldn't be a line side connection if you connect to the load side.....

Ok reread, I get it. That's a common question. I was going "the other direction".

I had a couple different responses typed up reading a few times with different understandings. Then I realized it didn't matter which scenario was in play because the utility (POCO) is always on the line side.

 

[SolarPro]

It's actually the same rule of thumb that I posted, only worded differently.

Carultch's rule of thumb applies on the dc and ac sides of an inverter. That makes it a great mnemonic device for people attending beginning/intermediate solar classes or new solar apprentices.

 

[iwire]

Carultch's rule of thumb applies on the dc and ac sides of an inverter. That makes it a great mnemonic device for people attending beginning/intermediate solar classes or new solar apprentices.

I can understand someone being confused which way to wire the AC side switch with its bi directional nature but if someone has problems figuring it out on DC side I would say that no mnemonic is going to help.

 

[SolarPro]

Word.

 

[Carultch]

I can understand someone being confused which way to wire the AC side switch with its bi directional nature but if someone has problems figuring it out on DC side I would say that no mnemonic is going to help.

One trick when you are drawing AC disconnects on a single line, is to go out of your way to draw it with the line side at the top. So if your feeder is depicted horizontally on the page, or if your feeder has power flowing down the page from the inverter to the utility, draw the line side of the disconnect at the top of the page and articulate the feeder lines around the disconnect symbol to show that its wiring orientation is intentionally specified one way.

I've seen it happen where it is not built properly, because the wiring orientation was not immediately obvious. A difficult fix when the line side is permanently energized, as is the case in a supply side connection.

 

[mwm1752]

I am a bit concerned of the OP working a megawatt system & does not know line from load.

 

[SolarPro]

I am a bit concerned of the OP working a megawatt system & does not know line from load.

Except there is no load. With a parallel power system, you have two sources. This question is fairly common even among experienced electrical engineers and electricians when they first encounter an interactive system.

 

[Carultch]

Except there is no load. With a parallel power system, you have two sources. This question is fairly common even among experienced electrical engineers and electricians when they first encounter an interactive system.

Similar to how I've asked how to know which side to call primary vs secondary of a backfed transformer. Obviously I know what primary and secondary mean in general, but when aren't building a conventional system where power only flows from the utility, it isn't as simple to choose your vocabulary.

 

[Joelengrahm]

Line side taps are not allowed only line side connections

 

[mwm1752]

Except there is no load. With a parallel power system, you have two sources. This question is fairly common even among experienced electrical engineers and electricians when they first encounter an interactive system.

Interesting -- a megawatt system in parallel with utility to serve a structure did not get that from the OP -- generally I would assume the megawatt system is serving the utility such as a solar farm.

 

[ggunn]

Interesting -- a megawatt system in parallel with utility to serve a structure did not get that from the OP -- generally I would assume the megawatt system is serving the utility such as a solar farm.

It happens. We recently put in a 812kW PV system on the parking garage of a hospital. It is interconnected on the load side of the hospital's MDP.

 

[Carultch]

Line side taps are not allowed only line side connections

What's the difference?

The formal name is unclear for that section of conductor between the line side disconnecting means for solar, and the service conductors. Tap is simply one of the relatable terms we have.