Phase Monitor on the Line Side of the Main Switch

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FoxValleyRob

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Sugar Grove, IL
I'm having a challenge with some installing contractors/ComEd regarding phase monitoring equipment that the Owner requested on the incoming main lines.

The Owner wants to monitor the condition of the incoming utility service while the main switch is potentially in the off position, to determine that the power quality is adequate to apply it back to his distribution. I can't find any NEC code that disallows this, but the controls contractor is up in arms, complaining that it is an unsafe design. He also convinced the local utility company (ComEd) to "disapprove" the design, as the line side of the disconnect switch is "owned by ComEd".

My point of view is this...The line side of the main disconnect is already metered (past the C/T cabinet), and the main switch is located within the Owner's switch gear. I feel the Owner has the right to monitor the power quality of the incoming service, and the utility company should have no say in it.

Anyone else have any insight to offer?


Thanks!
 
Besoeker

Besoeker

Senior Member
Location
UK
FoxValleyRob said:
I'm having a challenge with some installing contractors/ComEd regarding phase monitoring equipment that the Owner requested on the incoming main lines.

The Owner wants to monitor the condition of the incoming utility service while the main switch is potentially in the off position, to determine that the power quality is adequate to apply it back to his distribution. I can't find any NEC code that disallows this, but the controls contractor is up in arms, complaining that it is an unsafe design. He also convinced the local utility company (ComEd) to "disapprove" the design, as the line side of the disconnect switch is "owned by ComEd".

My point of view is this...The line side of the main disconnect is already metered (past the C/T cabinet), and the main switch is located within the Owner's switch gear. I feel the Owner has the right to monitor the power quality of the incoming service, and the utility company should have no say in it.

Anyone else have any insight to offer?


Thanks!
Click to expand...
How would you maintain/repair it?
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Besoeker said:
How would you maintain/repair it?
Click to expand...

good question.

why does the owner feel is is necessary to check PQ before turning power on? is someone going to run out and shut off the main switch every time you get a power blip?

what happens if PQ goes in the dumper while the switch is closed?
 
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FoxValleyRob

Member
Location
Sugar Grove, IL
it has a 30A 3P disconnect switch ahead of the meter, with 5A fuses, to protect the meter, and to disconnect it from the system when necessary.
 

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Jraef

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
FoxValleyRob said:
it has a 30A 3P disconnect switch ahead of the meter, with 5A fuses, to protect the meter, and to disconnect it from the system when necessary.
Click to expand...

That arrangement is SOP with a lot of remote pump stations I have worked on. The Phase Monitor will be used to Shunt Trip the main CB, but they don't want anyone being able to re-close it if the phasing is still incorrect. Where I've seen it used is on far flung deep well pump stations with submersibles where the bowl of the pump is held on with a king nut and if the pump EVER starts backward for even a second, the keeper on the king nut can break, the nut spins off and the pump bowl is lost to the bottom of the well. The reason they have to guard against it is that they may have multiple portable backup generators owned by different entities (like water depts. and fire depts.) with the possibility that someone connects one where the phasing is backward, or occasionally in a storm the utility linemen will accidentally reconnect downed lines out of sequence.

The operative issue is that the Phase Monitor must have it's own OCPD, which in your drawing it does. The comment about the utility "owning" the line side of the breaker is pure bunk. That's why we have the "six hand rule", you are allowed up to six devices acting as main power disconnects in a service as long as they are all in the same place.
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Jraef said:
That arrangement is SOP with a lot of remote pump stations I have worked on. The Phase Monitor will be used to Shunt Trip the main CB, but they don't want anyone being able to re-close it if the phasing is still incorrect. Where I've seen it used is on far flung deep well pump stations with submersibles where the bowl of the pump is held on with a king nut and if the pump EVER starts backward for even a second, the keeper on the king nut can break, the nut spins off and the pump bowl is lost to the bottom of the well. The reason they have to guard against it is that they may have multiple portable backup generators owned by different entities (like water depts. and fire depts.) with the possibility that someone connects one where the phasing is backward, or occasionally in a storm the utility linemen will accidentally reconnect downed lines out of sequence.

The operative issue is that the Phase Monitor must have it's own OCPD, which in your drawing it does. The comment about the utility "owning" the line side of the breaker is pure bunk. That's why we have the "six hand rule", you are allowed up to six devices acting as main power disconnects in a service as long as they are all in the same place.
Click to expand...

The drawing shows the main as a BPS - presumably bolted pressure switch. i don't think there is any way to put a shunt trip on a BPS.
 
Jraef

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
petersonra said:
The drawing shows the main as a BPS - presumably bolted pressure switch. i don't think there is any way to put a shunt trip on a BPS.
Click to expand...
Yes, there is. That's why a BPS is different from a Knife Switch disconnect; it CAN have a ST, which is mandated if above 1000A (because of the need for GF protection at that level and above).
 
Jraef

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
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FoxValleyRob said:
The CT's are rope CT's that wrap around the conductors...so no direct connection. I'm pretty sure that won't be an issue...
Click to expand...
OK, so Rogowski coils. Then yes, that's true, no need to short them out*. We didn't know that from your drawing though.

*(for those unfamiliar, Rogowski coils are inherently current transducers, not transformers, so the output is 0-5VDC going to the meter and you remove them by splitting the "rope" in a Y connector)
 
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jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
FoxValleyRob said:
He also convinced the local utility company (ComEd) to "disapprove" the design, as the line side of the disconnect switch is "owned by ComEd".
Click to expand...

There are several NEC articles that support this type of installation.
The first is the '6-disconnect rule' where multiple main switches are allowed. And, there is the allowance for metering and monitoring circuits.

If current measurements are being made, there is absolutely no reason for the CTs to be on the line side of the main switch. There will be no current flowing if the main switch is open, therefore voltage measurements need to used to determine 'main' phase loss and phase reversal
 
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