# 5 Pole, 3-phase

#### Dave0707

Joined Apr 14, 2015
8
Good morning all,

My company just purchased a new machine and I need a little help with the electrical connections.

The machine is rated for 208 volts 3 phase but it must have 5 wire with a neutral and ground (Y configuration). Internally, the voltage is split into 3 separate 110v circuits

I currently have a 208v 3 phase 4 pole electrical drop in the location where there machine will be located. Can I simply install a grounding rod where I want to place the machine for the 5th pole (ground)?

#### BR-549

Joined Sep 22, 2013
4,938
What is an electrical drop?
Do you mean a disconnect?
What country are you in?

Joined Jan 15, 2015
5,362
It would be nice to know your location. However in the US my first suggestion would be to consult the NEC (National Electric Code). It sounds like you have a 5 wire 3 phase 208 volt WYE configuration. Phase to phase is 208V and any phase to neutral will be 120V. Worked out as 208 / 1.732 (Sq Root of 3) = 120. You have your 3 phases typically L1, L2 and L3, Neutral and a Ground (Neutral and Ground are tied or Bonded together). As to a Grounding Rod any grounding rod in the US must comply with the NEC. Rather than suggest anything if you are in the US I just suggest consulting the NEC.

Ron

#### JWHassler

Joined Sep 25, 2013
280
If you have a legal 208/120 drop, it has that fifth "wire" already: it's called the grounding conductor, or just "ground."
The fact that you asked about a ground-rod is a bit bothersome: you need to talk to an electrician.

Joined Jul 18, 2013
20,456
Generally a 3ph star secondary has 3 phases, star point as neutral, this would be connected to an existing service ground, making 3ph N & Gnd.
Placing a ground rod at the machine is redundant if the star point is not at Gnd potential.
Max.

#### Dave0707

Joined Apr 14, 2015
8
By electrical drop I mean we have a plug on a cord, with 4 poles. The shop is located in New York, on Long Island, not in NYC.

I have 4 wires going to this location, I need to connect to a NEMA Type L21-30R, which is 5 wires. So do I need to run a separate ground to this plug?

Joined Jul 18, 2013
20,456
What do you meant by 3phase 4 pole?
3ph and neutral?
Max.

#### Dave0707

Joined Apr 14, 2015
8
Correct. Currently I have an L15-20 plug with 4 wires (L-L-L-N). My new machine requires an L21-30 (L-L-L-N-G). Where do I get the ground from?

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Joined Jan 15, 2015
5,362
By electrical drop I mean we have a plug on a cord, with 4 poles. The shop is located in New York, on Long Island, not in NYC.

I have 4 wires going to this location, I need to connect to a NEMA Type L21-30R, which is 5 wires. So do I need to run a separate ground to this plug?
The ground should be run from the service panel (the source). In some cases depending on the machine or whatever you are powering you need a bus drop and a service disconnect, in some cases a plug and socket can serve as the service disconnect. This is why I and others have suggested an electrician familiar with the code and how it will apply to what you have. Your problem as I see it is hat your service for 208 volt wye should run to the machine with 5 wires and you only have 4. I don't think sinking a ground rod is a viable solution.

Since you are on LI, give my regards to Uniondale.

Ron

#### tcmtech

Joined Nov 4, 2013
2,867
Although not always acceptable, but still often used in these situations, is to tie the original 4th lead for common to the new ground on the receptacle side of the socket and plug set so you have a 5 wire socket for your 5 wire plug.

Its sort of like upgrading the old three wire single phase sockets where common and machine ground shared a common connection and line at the machine to the newer four wire ones where common and ground are separate in the machine cord. The four wire to three wire change back is done in the socket so everything looks and works right.

Joined Jul 18, 2013
20,456
I currently have a 208v 3 phase 4 pole electrical drop in the location where there machine will be located. Can I simply install a grounding rod where I want to place the machine for the 5th pole (ground)?
When you say you have 3ph and N drop, do you mean this is the principle supply to the building? and if so where does the supply originate?
Max.

#### Dave0707

Joined Apr 14, 2015
8
I pass Uniondale everyday. We are out in Farmingdale!

I was thinking of connecting ground and neutral at the plug, but since most of my CNC's (hardwired) have a grounding rod, I thought this would be an acceptable method as well.

I have several different supplies to the building, but this drop comes from the 208 electrical panel. All of our twistlock connections are 4 wires.

Joined Jul 18, 2013
20,456
I would have expected the star point to be referenced to ground, regardless of its origin, are you sure there is not a ground in the panel that you could originate from.
BTW, the book considered the 'Bible' on grounding is the Soares Book on Grounding, used as a ref by international code regs Published by the Intnl Assoc of Electrical Inspectors.
I got a copy in 100% shape from AbeBooks clearing house for \$1.00!
Max.

#### Dave0707

Joined Apr 14, 2015
8
Fantastic. I just ordered it.
Inside the electrical panel, the Ground leads are the neutrals on for the Plugs. I would prefer to ground this machine to a separate ground, and leave the neutral as-is. It seems as if I would need to get a ground from another location, just not sure where.

#### ErnieM

Joined Apr 24, 2011
8,040
I'm on the island too and just want to point out that 2 out of 5 boroughs of NYC are located on Long Island.

It’s kinda why Long Island City in Queens is called LONG ISLAND CITY.

</rant>

#### BR-549

Joined Sep 22, 2013
4,938
Service cord. I have not heard it called a drop.

It would be nice to see pic of installation space.

A lot of times, just installing the equipment, will ground it.

I would plug it in and ground anywhere.

Joined Jan 15, 2015
5,362
Here is what you have:

This is what you are looking at:

Neutral and Ground are bonded (tied) at the service panel in the 5 wire configuration. Since you have the first cartoon up there you could simply tie the Neutral to the center ground pin in your receptical. The reason I have not suggested doing so is because I am not sure how the NEC code would view doing that. Been some years since I played IE (Industrial Engineer). I don't have a clue if tying those two together would be Kosher if anything ever went wrong. Will it work? Yes, in a word.

I was Uniondale born and raised, well actually Brooklyn born and grew up in Uniondale during the 50s and 60s. I get back every year for a party we have at Lido Beach under the mushrooms. This year it will be July 25th. The Uniondale of today is nothing like when I grew up. Hell, very little of LI is.

Ron

Joined Jul 18, 2013
20,456
I have always been under the impression that re-referencing the neutral to ground other than the service source is definitely not allowed per NEC CEC ?
If a local ground rod is used it should also be bonded to the service ground conductor.
Another alternative allowed is where galvanic isolation occurs, the isolated supply can be re-referenced to earth conductor at the isolated source ONLY.
Max.

#### Dave0707

Joined Apr 14, 2015
8
I will try to upload a few pictures later today.
If I tie in the Ground and the Neutral to the plug, wouldn't I be getting some sort of feedback from my other equipment? For this reason, I suggested the grounding rod. This is a Laser Marking machine, I am not sure how sensitive the components are. We have one laser marker already but that unit runs on 220V.