ECN Forum Forums General Topics of the Trade General Discussion Area 3-Phase Power

Hey there,

I'm not an electrian, and didn't pay enough attention in physics in college...

The company I work for has just taken over new space that has an existing 3 phase mains. The distribution board has a 200 amp mains breaker, and then is broken out into a dozen 20 amp single phase circuits.

I assume it was standard wiring, splitting the three hot wires up evenly (I am assuming it's 4 wire).

The issue is that the building management company wants to charge for 600 amps. They claim that we can utilise 600 amps as it is right now (without changing any breakers, wiring, etc).

They are unwilling to meter and charge per kWh as we'd prefer.

My limited understanding of 3-phase is that while the physical cables might be capable of transporting the load, the breaker should still trip beyond 200 amps. Right?

Or does the breaker snap only if one of the legs exceeds 200 amps and you really can run 500+ amps?

If any individual phase of a three phase breaker exceeds the trip value (200A in your case), it trips all three together. So theoretically in a lab, you could draw 600A if your loads are phase to neutral and perfectly balanced.
Many leases include a cost for electricity based on square footage of the space occupied or a sub meter.

I am not a law proffesor, but I am under the belief, the land management company cannot resell electric for a profit.

I am told there are laws against this, you may want to investigate this. I have never heard of charging you not on your use but what COULD be your use.


Dnk...

Might I suggest.... (Why am I saying this, I hate them.) An E-Mon/D-Mon, a metering device, that you can monitor your power/Kw usage with. That way you have an idea if you're getting a good deal or not. And have some numbers to go back to your leasor with to renegotiate with. It's that worrd, "renegotiate", everytime I install an E-Mon/D-Mon, I know I am stuck in the middle of someones renegotiation. Thats why I hate them....

FYI - A 200A 3 phase service is just that, not a 200AX3 = 600A service. It would be a misrepresentation to call it anything else. Wish you luck.

So, realistically, since this is not a perfect lab environment.. what should I expect in terms of balance?

Personally I can't see this as a justifiable way of billing.. bleh.. ah well.

You can only get realistic information once you meter your loads, and understand the profile.

You know, re-reading this has got me thinking here.

I can only speculate that the land management company, if they do not want to meter your usage, and bill you accordingly, in turn they want you to pay for something your not using.

Why wouldn't they meter you usage?

It doesn't sound right to me.


Dnk.........

Hugh, to get a well informed opinion, please do a little more informing. How do they want to charge you? by the KWHR? and if so, how are they figuring it? Very well could be that there is a misunderstanding of intentions here and people are calling something one thing when they meant another if they knew what they were talking about in the first place. Because depending on how you are doing the math, charging for 600 amps and 200 amps may be the same thing. This whole thing just sounds a little too wierd.

We meter our usage per circuit very carefully. Each circuit goes into a network based PDU that meters each subsequent outlet (each typically has 8 outlets).

The building management is providing us with clean power, redundant feeds from the grid, and a battery backup system. For redundancy purposes, they do need to know how much we intend to use so that they have the appropriate battery stores.

But they want to bill us for 600 amps when we only have TWELVE 20amp circuits in the box. Our usage is currently around 90amps, and even if they charged us for 240amps (still above the 200amp mains breaker) we'd be happier.

Another method of billing in a datacenter/webhosting facility is to charge per branch circuit of UPS power. This way they can set aside a certain amount of capacity in the PDU for your load and you use the branch circuit as you wish.