Panel overheating

[larmee]

Thanks in advance for any help. I have a problem child at a major department store here in my hometown. In the beginning there were 4 ac units that were being feed from a 480 switchgear. Someone in the near past replaced these 4 units with 208 volt units feed with number 10 wire on 3 phase 30 amp breakers. The panel that now feeds these units is has a 225 amp rated bus fed from a 45 kva transformer. Initially the secondary voltage was operating at a very low voltage. The secondary of the transformer was producing around 199 volts and I changed the tap and increased the voltage by about 10 volts and that helped 3 of these units. One of the units continues to trip and the entire panelboard as well and all breakers are very hot to the touch. I did an amprobe reading and am getting around 105 amperes per phase but that is not the entire load. There is a bailer on a 40 ampere 3 phase breaker that runs momentarily as well as a few other minor loads. It is my recommendation to the customer that the 45 kva xfmr be increased to a 75 kva. The ac units are pulling around 26 -28 amperes per phase. I know that is borderline but with the 45 kva xfmr there I don't have much wiggle room to increase the ampere rating for the units. I suspect that someone changed the units and added them to this panel without do much homework. I have as well changed all the ac unit breakers and that has helped up until now but this heat problem needs to go away.
:slaphead:
Many thanks,

 

[jim dungar]

Hot to the touch does not mean anything, get a thermometer.
The operating handles of fully loaded breakers can get to 60?C (140?F), fully loaded lugs run around 50?C.

 

[larmee]

Hot to the touch does not mean anything, get a thermometer.
The operating handles of fully loaded breakers can get to 60?C (140?F), fully loaded lugs run around 50?C.

In my opinion a correctly operating system should not be hot to the point that you could not continuously hold your hand to it. There is an obvious problem with the system.

 

[iceworm]

... The secondary of the transformer was producing around 199 volts and I changed the tap and increased the voltage by about 10 volts and that helped 3 of these units. One of the units continues to trip and the entire panelboard as well and all breakers are very hot to the touch. ...

That's good you turned up the voltage.

...replaced these 4 units with 208 volt units feed with number 10 wire on 3 phase 30 amp breakers.
... The ac units are pulling around 26 -28 amperes per phase. I know that is borderline but with the 45 kva xfmr there I don't have much wiggle room to increase the ampere rating for the units. ...

Changing the transformer won't cool off the panel. The panel is plenty big enough. If it is infact too hot, then there is something wrong with the panel - loose connections, small wire, oxidized CB connections, maybe even undersize CB that are run right at the trip setting. Fix these first.

Forget "wiggle" room on the transformer. Increasing the AC CBs won't cause any additional overload to the transformer. For a 26A - 28A load, 30A CBs are too small. The #10 wire is likely too small as well. Check the equipment nameplates. Size the circuits to the nameplate data, and pay attention to the circuit length. Maybe the one that is tripping is long enough the Voltage drop is getting to it.

Do a load calc on the panel. If it is more than the 45kva transformer can put out, then consider changing the transformer.

ice

 

[Cow]

Check the equipment nameplates.

Do this first. Then a load calc of everything in the panel. That'll get you started.