3 Phase, 3 Wire MSB board

Status
Not open for further replies.
P

pecksus

Member
Location
Derby, KS
Occupation
Electrical Engineer
I have an old Federal Pacific MSB with a nameplate rating of 3 phase, 3 wire but several of the panels it feeds have neutrals. Where does the neutral terminate at the MSB?
 
Bwas said:
It's pretty normal in my experience. Federal pacific seems to have been common when neutrals and grounds were intermingled all over the place.
Click to expand...
Bonding a feeder neutral to the 3Ø, 3-wire main switchboard enclosure is normal?
 
I should clarify, it is a 1600A., 208v, 3ph., 3w. switchboard downstream of the Main 480v. Switchboard at a huge shopping mall. But there are 208/120v. panelboards being fed out of this switchboard so where is the neutral coming from? A field installed neutral bar sounds plausible - and that is connected to a ground rod? I will just have to go look. Thanks for all the comments.
 
pecksus said:
I should clarify, it is a 1600A., 208v, 3ph., 3w. switchboard downstream of the Main 480v. Switchboard at a huge shopping mall. But there are 208/120v. panelboards being fed out of this switchboard so where is the neutral coming from? A field installed neutral bar sounds plausible - and that is connected to a ground rod? I will just have to go look. Thanks for all the comments.
Click to expand...
Someplace, somewhere the center point of the 208 is bonded or earthed. Hopefully they aren’t using building steel or conduit as the neutral return path, but it wouldn’t be the first time. I would think your line to neutral voltages would be all over the place if it was only a rod.
 
The reason I said it might have a field installed Neutral bar is that someone may have purchased it as a 3 wire switchboard, so that’s what the nameplate says, but when the electrician installed it, he knew what was needed and rather that send it back, just installed a proper neutral kit. 3 wire on a 208V switchboard would only make sense if 100% of your loads were 3 phase, in which case using 208V would be stupid. It’s more likely though that the mistake was made by a purchasing agent, not a professional electrician.
 
You are correct. There is a field installed neutral bus bar in the switchgear that is bonded. It was probably installed at the time the gear was installed because it looked to be the same "age". Kinda surprised I haven't seen this before now.
Thanks.

BTW - You have won an all expense paid trip to Dodge City, KS but you have to collect in the next 60 seconds or the offer is withdrawn.
 
Sounds like was never code compliant from day one. If supplied by a feeder should have had separate neutral and EGC. If the feed to a separate bulding/structure could possibly have bonded the neutral at the separate building, but should still have had equipment that was suitable for use as service equipment - basically meaning an insulated ground bus with optional bonding jumper where necessary.

As was said lot of FPE was installed at a time when there was a lot of mixing of neutral and EGC (even if it wasn't correct) and many installers I don't think knew any better in those times.
 
kwired said:
With the enclosure and metal raceways carrying the neutral beyond there or just an improper bond of the grounded conductor?
Click to expand...
Improper bonding. In my experience it is not uncommon to see grounds and neutrals freely intermingled in older facilities. I would say it is most common in commercial type structures.
 
Bwas said:
Improper bonding. In my experience it is not uncommon to see grounds and neutrals freely intermingled in older facilities. I would say it is most common in commercial type structures.
Click to expand...
I notice a fair amount of that kind of thing from that time period as well.
 
Status
Not open for further replies.
Top