ECN Forum Forums General Topics of the Trade General Discussion Area 3-phase no nuetral problem

bot540, I have a few questions for you, regarding this Project:


1: Are there 2 individual Services - meaning there are 2 separate gear sections, each one has a kWh meter and a Service Disconect, or is there only one gear section with a kWh meter + Service Disconnect?

2: How close is the gear section without the common grounded neutral conductor, from the gear section with 4 wires?

3: If bringing a grounded conductor into the 3 wire gear section is close to impossible, would an option to drive 3 Phase 3 Wire, or Single Phase 2 Wire (208VAC) equipment from the 3 Wire gear section be feasable?

4: When you say "The Service With The Neutral Is Maxed Out"; does this mean:

***A: The Service's Capacity is inadequate for the connected loads (as viewed by load calcs against the gear's rating &/or the Main Breaker of the system),

or...

***B: The Transformer feeding this Service Section has a lower kVA rating, than what will be required for the new connected loads,

or...

***C: There are no more spaces available for Circuit Breakers.

5: Can you see the Transformer which is feeding the Tenant Suite on your project?

If Transformers mounted on poles, are all 3 the same size - with only one wire coming from the "right side" secondary bushings on each Transformer, and a "common" wire, connected to each of the "left side" secondary bushings on each Transformer, which also comes off the Transformer on the left side, and is run with the 3 other wires?
This indicates a 4 wire Wye connection.

If you only see 2 Transformers, and they are connected together "in parallel", you have an open delta.

If there are 3 Transformers, with the "Middle" Transformer being twice as large as the outer 2 - and they are all connected 'in parallel", this is a closed delta.

In either delta case, if the "larger" Transformer has 3 wires connected to the secondary bushings, the system is a 4 wire delta (or a 3 wire with center tap ground).
If one Transformer has only 2 wires made up to the bushings, this is likely to be a 3 wire Delta.

6: If you are able to find the Transformer which feeds the Tenant Space, can you follow the Service Feeders to the point of attachment on the premisis?

*If Overhead: Does the drop from the Transformers / Pole attach to a riser, and from there get tapped into 2 separate risers?
Also, how many conductors?

* If Underground: Lift up one of the access covers on the Pad (in front of the Transformer), and see how many Service Feeder ducts run to your project (do not enter the Vault!!!).

Your scenario sounds like a very commonly done "Dual Service" option, found in buildings circa 1950's thru 1970's - having a Service Capacity not exceeding 400 amps per "Section".

These have two individual Service Sections - each with a kWh meter and Service Disconnect.

One Section is named "Lighting", and is the Service Section with the Grounded Conductor used + bonded to equipment and G.E.S.

The other Section is named "Power", and uses only the 3 Ungrounded Conductors.
It's enclosure + equipment is bonded to the "Lighting" Section via Equipment Bonding Jumper only - no system conductor is Grounded nor bonded at this service section.

The typical way of feeding the separate sections, is to use separate feeders + ducts for each service section, and the "separated feeders" get tied together either at the pole, in the Vault of a Pad Mounted Transformer, or just outside of the Weatherheads of 2 separate overhead service risers.

Granted, these were normally 120/240V 1 Phase 3 Wire "Lighting" Sections, and 240V 3 phase 3 Wire "Power" Sections, but I have also seen a few with 208Y/120V 3 Phase 4 Wire "Lighting" Sections, and 208V 3 Phase 3 Wire "Power" Sections.

Anyhow, let me know what you find out.

p.s. post those images!!!

Scott35

Is the neutral required for metering?

Or is it that the neutral, the main bonding jumper and the ground rod connection are sometimes made in the metering equipment?

LarryC

The ground electrode sometimes ends up in the metering equipment around here and they might have terminated the neutral there.

It makes me wonder, with a Wye service, why the Neutral doesn't come into a busbar in the main panel.
Sure from there, you can set up a load in Star or Delta.
Having a Neutral bus would help in the panel.
Just my thoughts.

I did a little more investigating and found out that "live front services" are illegal in The City of Chicago. I have decided the only work I will do on it is to change it out completely before adding anything else. Scott if I go back there I will look at the transformers. I will also get pictures.