Mystery Solved, plus a question (photos)

busman

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
All,

If you remember my post about the church with the single phase service and the three phase gear. Photos below show what I had expected all along. Details in words:

  1. No CT's in the CT cabinet
  2. 200A service conductors
  3. Illegal jumper in the MDP
  4. Didn't trace the red taps in the MDP mains
1743438145623.png
1743438167410.png
1743438202589.png

It is pretty clear this used to be three phase service with CT. Is it possible the PoCo dropped the three phase for some reason? This church was probably a very low usage customer (only on Sundays). There is 3-phase along the road less than 80 yards away where this is fed from. I could try to get it back to 3-phase, but they may have appliances that won't like 208V (AC units).


My question is, if I remove the clearly illegal jumper between A and C phases and replace with a three opening Polaris tap, will there be any other violations?

Thanks,

Mark

Note: Somehow the last photo got flipped left for right. The feeders really enter from the left.
 
The conductors need to be protected at their ampacity. Whether by a jumper or Polaris, a conductor isn't properly protected if it connects to 2 poles of the breaker
 
OK, so if I correct the jumper at the MCB and then do proper jumpers at each of the panelboards (only using two wires at each panelboard, that would get rid of the parallel feeders and then be legal, correct? Please let me know if I should draw a diagram to be more clear.

Thanks again,

Mark
 
busman said:
OK, so if I correct the jumper at the MCB and then do proper jumpers at each of the panelboards (only using two wires at each panelboard, that would get rid of the parallel feeders and then be legal, correct? Please let me know if I should draw a diagram to be more clear.

Thanks again,

Mark
Click to expand...
I made a drawing just to get it straight for me, if nothing else. Obviously the jumper between A and C would be done with a Polaris and the third "phase" wire would be capped off. Thoughts?

Thanks again,

Mark
 

Attachments

  • Church.jpg
    Church.jpg
    20 KB · Views: 10
Down stream of the meter, I would cut in a gutter, install polaris taps, then make sure they are re-feeding a MCB that is properly rated. IF not, then reuse the old CT cabinet space for a fused disconnect(s). By converting that cabinet into gutters or boxes.

I would verify the load, the bonding is the right size and where the GECs are bonded. You might need to fix those things as well.

busman said:
OK, so if I correct the jumper at the MCB and then do proper jumpers at each of the panelboards (only using two wires at each panelboard, that would get rid of the parallel feeders and then be legal, correct? Please let me know if I should draw a diagram to be more clear.

Thanks again,

Mark
Click to expand...

Are they feeders or parallel service conductors? They are tapped ahead of that MCB.

If feeders then replace breakers with a larger size and tap load side of that breaker to a fused disconnect to refeed whatever it was going to. Or install small panelboard with MCB. I can't tell what the space looks like.
 
Elect117 said:
Down stream of the meter, I would cut in a gutter, install polaris taps, then make sure they are re-feeding a MCB that is properly rated. IF not, then reuse the old CT cabinet space for a fused disconnect(s). By converting that cabinet into gutters or boxes.

I would verify the load, the bonding is the right size and where the GECs are bonded. You might need to fix those things as well.



Are they feeders or parallel service conductors? They are tapped ahead of that MCB.

If feeders then replace breakers with a larger size and tap load side of that breaker to a fused disconnect to refeed whatever it was going to. Or install small panelboard with MCB. I can't tell what the space looks like.
Click to expand...
Sorry. Brain pulled up the wrong acronym. I meant MDP. There is no MCB, it is the old six disconnect rule. Each of the six fused disconnects in the MDP has 100A fuses. What I'm proposing is to disconnect that illegal jumper in the MDP and have just two fuses in each disconnect feeding the single phase panelboards. At each panelboard, I would use a Polaris tap to have the two hot wires feed the three busbars. The only concern I have would be doing a load calculation since there is no MCB protecting the whole thing. Thoughts?

Thanks,

Mark
 
ramsy said:
How do you prevent unbalanced neutral overloads with 2/3 of the load on 1 leg?
Click to expand...
Not a problem if both legs are protected against overcurrent at their ampacity, and the neutral is equal sized. Or if the neutral is reduced, it is protected against overload by the load calculation.

busman said:
There is no MCB, it is the old six disconnect rule. Each of the six fused disconnects in the MDP has 100A fuses. What I'm proposing is to disconnect that illegal jumper in the MDP and have just two fuses in each disconnect feeding the single phase panelboards. At each panelboard, I would use a Polaris tap to have the two hot wires feed the three busbars.
Click to expand...
So if you have two ungrounded service conductors coming into the 3-phase MDP, and you just abandon the 3rd bus in the MDP and use it as a 2-bus MDP, that's fine. You could do the same at each subpanel as well. If you want to use the 3rd bus in one of the subpanels, you could energize it: either at the main lugs/main breaker via a 3 port polaris so that one incoming ungrounded supplies two poles (this is fine as long as the ungrounded conductor is protected against overcurrent at its point of supply), or by using a two pole breaker with the load side lugs connected together.

Cheers, Wayne
 
Here it’s pretty common to go from three phase (usually a delta or open delta service) on low load services. The local poco charges more per kWh for three phase, than single phase, so the customer has it changed to get the cheaper rate. Usually the only three phase loads are hvac, and it’s cheaper to replace with single phase units when the three phase units crap out.
 
ramsy said:
How do you prevent unbalanced neutral overloads with 2/3 of the load on 1 leg?
Click to expand...
The combined A-C legs cannot draw more current than the single upstream overcurrent protective device allows, so the neutral cannot be overloaded. While appearing similar, this is not the same as the issue of putting both legs of an MWBC on the same phase, where two different OCPD are involved.
However, I do not know of any manufacturer that would sanction the OP installation.
 
jim dungar said:
The combined A-C legs cannot draw more current than the single upstream overcurrent protective device allows, so the neutral cannot be overloaded. While appearing similar, this is not the same as the issue of putting both legs of an MWBC on the same phase, where two different OCPD are involved.
However, I do not know of any manufacturer that would sanction the OP installation.
Click to expand...
Yes I see, service / feeder fuses & neutrals get the same current.

However, with A-C legs combined multi-pole breakers encounter single phasing.

2-pole breakers with same leg across A-C wont run loads requiring opposite legs.

2-pole MWBC neutral current wont cancel with A-C legs combined. Un-fused branch neutral will burn up w/ twice the rated current.
 
ramsy said:
Yes I see, service / feeder fuses & neutrals get the same current.

However, with A-C legs combined multi-pole breakers encounter single phasing.

2-pole breakers with same leg across A-C wont run loads requiring opposite legs.

2-pole MWBC neutral current wont cancel with A-C legs combined. Un-fused branch neutral will burn up w/ twice the rated current.
Click to expand...
I should not need to worry about single phasing on the 2-pole CB's since it's already wired with A-C phases joined; I would just correct it to prevent overcurrent in the neutrals.

I will make it a point to look for MWBC's, but this can happen in any single phase panel where installers don't know to hit opposite phases - seen it more times than I can count.

Thanks,

Mark
 
hillbilly1 said:
Here it’s pretty common to go from three phase (usually a delta or open delta service) on low load services. The local poco charges more per kWh for three phase, than single phase, so the customer has it changed to get the cheaper rate. Usually the only three phase loads are hvac, and it’s cheaper to replace with single phase units when the three phase units crap out.
Click to expand...
Bingo!
That's what we have often. There are several two pot banks with a transformer we dropped around our system for that exact reason.
 
busman said:
I should not need to worry about single phasing on the 2-pole CB's since it's already wired with A-C phases joined; I would just correct it to prevent overcurrent in the neutrals.
Click to expand...
It is wiser to document the increased hazard not insureable, and recommend abatement where required.

However, no documentation is valid without demonstrated action that separates your work from the hazard.
busman said:
I will make it a point to look for MWBC's, but this can happen in any single phase panel where installers don't know to hit opposite phases - seen it more times than I can count.
Click to expand...
Saw 7 different accident attorney commercials on KTLA evening news in the last hour. The best customer testimonials explained other attorneys only get $300k, but Domingez Brothers got me 1.3 Million, with no fees guaranteed if you don't win.

Where is your project located? I can't lose by calling Domingez Bandidos right now.
 
ramsy said:
It is wiser to document the increased hazard not insureable, and recommend abatement where required.

However, no documentation is valid without demonstrated action that separates your work from the hazard.

Saw 7 different accident attorney commercials on KTLA evening news in the last hour. The best customer testimonials explained other attorneys only get $300k, but Domingez Brothers got me 1.3 Million, with no fees guaranteed if you don't win.

Where is your project located? I can't lose by calling Domingez Bandidos right now.
Click to expand...
The good news is it is NOT my project. I am just advising the Church Council as a volunteer. I am not accepting any money from them.

Mark
 
You must log in or register to reply here.
Top