480VAC to neutral (277V) wiring

Rson · Jan 28, 2020

Just want to check if the following is kosher.

Whomever did this motor control took a leg off 480 and use it to neutral for 277VDC to light up a pilot light.

This doesn't seem proper to me - is there any code this is violating?

View attachment 277VAC.bmp

parky · Jan 28, 2020

Not really, first of all the fusing is probably too large for a lamp.
The cables by the look of it would not take the fault current because of the fuse size etc. It would be better to take a link off one of the phases (main feed after isolator to a fuse sized for the application). Because it's just a light it should not alter the current balance of the 3ph to be significant.

kolyur · Jan 28, 2020

This could be permitted according to the NEC feeder tap rules in 240.21. The restrictions depend mainly on the length of the tap conductor. If it is 10 feet or less, you're OK as long as the wire is properly sized for the load (pilot light) and has its own overcurrent protection (you didn't say whether it did or not).

However, this application could still be a violation because the lugs on that fuseholder likely aren't rated for such a small wire. In a properly built panel, the feeder tap rules are usually applied to power distribution blocks that have line and load lugs sized appropriately for the wires terminating in them.

dogleg43 · Jan 28, 2020

A 277VAC pilot light? That’s how people get killed.

It is simply not a good idea to use high voltage for pilot/control wiring. Some farmers used to use 480VAC control wiring. You get so used to 24V or 120V controls and then you put your meter on a button an get 480V, wow!

Rson · Jan 28, 2020

dogleg43 said:
A 277VAC pilot light? That’s how people get killed.

It is simply not a good idea to use high voltage for pilot/control wiring. Some farmers used to use 480VAC control wiring. You get so used to 24V or 120V controls and then you put your meter on a button an get 480V, wow!

Yes, I agree completely.

However, I'm trying to find the code that states this is improper so I have something to back it up with.

rupej · Jan 28, 2020

The code violations were already mentioned. It's definitely not acceptable. And if you're going to go through the trouble to fix it, that's a good excuse to change to 24VDC while you're at it.

kolyur · Jan 28, 2020

Rson said:
However, I'm trying to find the code that states this is improper so I have something to back it up with.

Here are the relevant codes:
110.3(B) "Equipment...shall be installed and used in accordance with any instructions included in the listing or labeling."
110.14(A) "Terminals for more than one conductor...shall be so identified."

Find the part number for that fuse block and look up the spec sheet. Locate the wire gauge range for the lug... I'm pretty sure that little wire won't be within it... there's your justification.

jraef · Jan 28, 2020

rupej said:
The code violations were already mentioned. It's definitely not acceptable. And if you're going to go through the trouble to fix it, that's a good excuse to change to 24VDC while you're at it.

But still, to feed the primary of a control transformer or 480V power supply you need lugs that are rated for two wires and in this case, two dissimilar sized wires. so the distribution block is still necessary, plus room for it and wire bending space.

rupej · Jan 28, 2020

jraef said:
But still, to feed the primary of a control transformer or 480V power supply you need lugs that are rated for two wires and in this case, two dissimilar sized wires. so the distribution block is still necessary, plus room for it and wire bending space.

I agree. This looks like it's all inside of a disconnect switch. Hopefully there's room for all that in the panel that this feeds.

Rson · Jan 28, 2020

I found the conductor – a Belden 8760 which is only #18AWG. The disconnect is only applicable from 14 to 6 AWG, so this installation fails to meet NEC code by 110.3

If it were corrected by adding a new wire, this disconnect does not state that it allows more than one conductor, so it will fail code by 110.14.

If some distribution panel were added and the conductors were ok on that, it appears it would be ok per
NEC 240.21 (C), although it would have to be run in a raceway or conduit (this does not – the wires are exposed, I'll try to upload more pictures)

If it were then run in conduit, it appears 277VAC would still be allowed if I am reading correctly? The only violations are the conductor/terminal size and the fact that it is not run in raceway.

Thanks for all the help.

rupej · Jan 28, 2020

Rson said:
The only violations are the conductor/terminal size and the fact that it is not run in raceway.

Unless it's not fused after it leaves the disconnect switch, in which case it's violating maximum fuse size rules for the conductor size.

ValeoBill · Jan 28, 2020

Inspectors in my area only will allow one conductor under the lug UNLESS I provide documentation showing the lugs accept more than one conductor. Easier to tap to a low voltage xfmr for a 120v PL with proper wiring/fusing ...

Rson · Jan 29, 2020

Ok, so here is the deal.

I've found this type of hack wiring is in two different areas.

On one, I have a VFD on a gear motor, so I'm removing all the 277 and using the 24VDC on the VFD to run to the pilot lights.

On the second, oddly enough, I have a 480/120 transformer. I don't have space to add additional fusing, but they did fuse both the hot and neutral of the 120.

The transformer is a 750VA, which should require 4 1/2A fuses on primary and 10A secondary. The motor is 3/4HP, which could take a max of 3A fusing.

If I had a 500VA transformer, it would only require a 3A fuse. If that were the case, I suppose technically I could run the transformer tap without additional fusing and tap the wires at the transformer instead of the disconnect? (they are wire-lugged at the transformer with a bolt/screw connection)

Rson · Jan 29, 2020

To add to the oddities, the motor with the transformer is listed as:
0.75HP motor
60Hz
230/480VAC
4.2A / 2.1A FLA
SF 1.7

But 2.1A FLA @ 480 is a 1HP rating by electrical code.

That would let me have a 4 1/2 A fuse.

I found several matching pictures of the nameplate online:
https://static.wixstatic.com/media/a866f5_92c9752bdfdc4dc486c7b2192cfeab36~mv2.jpg/v1/fill/w_768,h_575,al_c,lg_1,q_85/a866f5_92c9752bdfdc4dc486c7b2192cfeab36~mv2.jpg

JesperMP · Jan 29, 2020

It seems to be a Grundfos ML71BB motor.
~~According to the manufacturer, it is to be connected in delta for 440-480V.~~
edit: Actually it is not delta. See the "wiring diagram" by the link above on how to connect it.
https://product-selection.grundfos.com/product-detail.product-detail.html?custid=GMA&productnumber=85900703
I think that the name plate is possibly labelled wrongly !!
On the website, the motor is rated at 0.75 kW, on the photo the label says 0.75 hp.
Whatever you do, the motor is rated at 2.1A (*) when connected as desribed, so you must protect it for 2.1A, definitely not 4.5A.

*: On the website, it says cryptically
"Rated current: 1.9 A
Maximum current consumption: 2.1 A"
So what is it, 1.9A or 2.1A ?
Anyway, it is defiitely not 4.5A

480VAC to neutral (277V) wiring

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