Electricians in the da house?

[Kat]

We just moved into the new shop Monday, and we are having electrical issues.

What is happening, is some of the 120v outlets are dipping to 114v even with no load. This is enough to freak out our CMM controllers. Under 115v they shut down to protect themselves.

The building is 480v 600amp 3ph 4 wire, and we have a dry distribution transformer that is 45kVA 208Y/120v 3ph 4 wire. Breaker for transformer is 70 amps, and main breaker for 208/120 panel is 150 amp. Measured voltage at panels are:

480 = 492 (Edison checked this)
277 = 283
120 = 121.5

Most outlets are 120/121.

So I pop open the bizarre Cutler Hammer 208/120 breaker panel (took an hour to figure out how), and see some stuff that gets my Spider Sense tingling:

1) There are 32 single phase power leads, and 20 neutrals servicing them.

2) Some of the breakers have 2 or 3 wires screwed into their single terminal.

Item #1, I don't know if that's OK. Item #2, pretty sure that is NFG.

Sidebar: 1/2 of our 120v load is computers (switching power supplies, non-linear load). Is it necessary to change the transformer to a K-rated (K=4 or K=13) or is that overkill?

(McRat, not Kat)

 

[Poltergeist]

The shared breakers are probably your problem. To much load on one breaker also possibly too much load on 1 line for the gauge wire to give you full 120.

If you are certain that there is no load on the breaker that controls the outlets you are having a problem with then the problem is probably a combination of distance from the panel and too small a gauge of wire. The only other thing I can think of that could cause is a bad connection somewhere with a wire nut.

 

[Randy5.0]

Pat,
Is this a new electrical install or a remodel? It sounds like a few circuits have been added to the panel and sometimes people just land the phase conductor on any old breaker they can make fit. Its not right but I see it all of the time. The other concern is they are sharing neutrals between the phases which can be done, but you have to be careful to not overload the neutral which is easy to do. It sounds like you need to have somebody clean up your branch circuits and balance the load between phases in your panel.

 

[Fingers]

We just moved into the new shop Monday, and we are having electrical issues.

What is happening, is some of the 120v outlets are dipping to 114v even with no load. This is enough to freak out our CMM controllers. Under 115v they shut down to protect themselves.

The building is 480v 600amp 3ph 4 wire, and we have a dry distribution transformer that is 45kVA 208Y/120v 3ph 4 wire. Breaker for transformer is 70 amps, and main breaker for 208/120 panel is 150 amp. Measured voltage at panels are:

480 = 492 (Edison checked this)
277 = 283
120 = 121.5

Most outlets are 120/121.

So I pop open the bizarre Cutler Hammer 208/120 breaker panel (took an hour to figure out how), and see some stuff that gets my Spider Sense tingling:

1) There are 32 single phase power leads, and 20 neutrals servicing them.

2) Some of the breakers have 2 or 3 wires screwed into their single terminal.

Item #1, I don't know if that's OK. Item #2, pretty sure that is NFG.

Sidebar: 1/2 of our 120v load is computers (switching power supplies, non-linear load). Is it necessary to change the transformer to a K-rated (K=4 or K=13) or is that overkill?

(McRat, not Kat)

The multiple wires into a single breaker isn't a big deal. The load is the load. As long as the terminal itself is not overstuffed and all the wires going into the breaker are sized properly for the breaker rating.

Check the voltage at the breaker terminals. IF that is good, you have a marginal connection down stream or the run is too long with too small a wire. If it is low, check that all your phase loads are balanced. (use a clamp on amp-meter.) Finally, make sure the neutrals are all properly bonded in the panels.

 

[Kat]

Thanks!

All voltage readings at the breaker terminals are over 120.

It looks like 3 people worked on the building:

The original builder (B+)
The contractor who did the office expansion (A+)
And Larry The Cable Guy at some later time (D-)

I found some circuits in the ceiling that were serviced by extension cords and power strips. And some other stuff that is VERY well done.

Crappola. Looks like the next step is to open up the ceiling again. That is where all the wiring goes. The run should be short (the building is under 100'), and the worst outlet is <40' from the panel. Now that the machines are installed and calibrated, I can't move them, and some of the bad outlet conduits are above machines. I did check voltages, but I guess I didn't do a good enough job.

The minute I discovered the issue, I ordered "double-conversion" UPS's for the delicate machines, and I will put them in today (they arrived Friday PM). For those that don't know, double-conversion UPS's (aka 'on-line' UPS) run off the battery 100% of the time, and the wall AC is used to just recharge the battery, or as a backup if the battery system fails. These will hold up full voltage regardless of wall outlet voltage. They have no switch-over time either. If the power goes out, they do not drop voltage briefly like a normal UPS does.

But a double conversion UPS is not a solution, it's a band-aid. All kinds of electric equipment has it's life cut short (even the UPS itself) if it has to deal with low voltage or fluctuating voltage.

What is odd though, is the voltage is down with all the 120v devices shut off. Got to be a bad connection. As per your posts, I checked all the connections at the panel, and gave them a "nudge", and the volts were still down. Now to check for wire nuts in the ceiling. If that doesn't work, I will string new 12ga hot+neutral to each bad outlet.

 

[Sledhead]

Thanks!

All voltage readings at the breaker terminals are over 120.

What is odd though, is the voltage is down with all the 120v devices shut off. Got to be a bad connection. As per your posts, I checked all the connections at the panel, and gave them a "nudge", and the volts were still down. Now to check for wire nuts in the ceiling. If that doesn't work, I will string new 12ga hot+neutral to each bad outlet.

With no load a bad connection (high impedance) won't have any voltage drop across it unless you have a VERY high impedance and a poor quality meter (low sensitivity or low ohms/volt rating).

Did you "nudge" all the neutral screws and all the breaker screws?

Make sure you are measuring the supply and receptacle breakers close to the same time. I have seen entire industrial parks have 125 V at lunch time and 114 V when lunch is over and all the machines start again.

As Fingers stated, it may be a load balancing issue amongst the phases or long branch circuits but not with the load off ??? I don't like the multiple wires into single breakers though, tends to screw up the thermal trip function.

Also, the transformer may have taps you can change. The primary side looks high at 492.

Always verify the meter is accurate.

With those online UPS's there will undoubtedly be harmonics radiating through your system. If you are looking at transfomers consider a zig-zag to cancel harmonics.