Electricity Meter rating

[Sparks]

Not strictly DIY, but anyway....

A friend of mine has an office, in that office there is quite a lot of halogen lighting, and probably 20 PCs, and 4 servers. They are soon to get aircon in the "Computer Room" (Basement!) The electricity meter is rated at only 40A (Single Phase) - The little disk inside is spinning at quite a high rate! (I think it was about twice per second, or thereabouts when I looked) They seem to have two consumer units, each about 20 way - both have a 100A isolator I have a clamp meter, so will test the load on it when I am next there. Should this be uprated, as I know my house supply is 80A! Would this usually be done free of charge by the electricity company?

I was also going to suggest looking into getting Economy 7, so the electricity used at night (Servers and A/C and people who leave their PC's on!) would be on cheaper electricity.

Sparks...

[Wanderer]

If the actual rating says 40amps then yes. If the name plate actually says 40LR then it's good for 80amps. As to E7, I can't remember the actual break-even point, but I seem to recollect that something like 23% or 27% of energy useage should be in the night period before it becomes cheaper to switch to E7.

[Owain]

"Sparks" wrote | Should this be uprated, as I know my house supply is 80A! | Would this usually be done free of charge by the electricity company?

I don't think they do anything free. If this 40A meter is at the end of a rather elderly main, the main might need upgrading. Possibly costly.

20 PCs at 100W is only 2kW. Changing to LCD screens will cut power consumption and also reduce the thermal load on the aircon. Low energy lighting would also reduce the thermal load compared to halogens. As this is a workplace, Electricity at Work Regulations will apply and the installation should be periodically inspected, with particular attention to the earth leakage of 20 PCs and screens which might be on one 32A ring circuit.

| I was also going to suggest looking into getting Economy 7, so | the electricity used at night (Servers and A/C and people who | leave their PC's on!) would be on cheaper electricity.

This would cost *more*, as E7 has a higher *daytime* rate. E7 only saves money if heavy consumption can be moved *off* daytime or 24-hour use and into the cheap rate period (hence storage heaters and stored water heating).

In an office, PCs, lights, electric kettle, handwash water heaters in the loos, non-stored electric heating, etc, will be used mostly during the day with very little night time use.

Owain

[Dorothy Bradbury]

o Economy 7 is quite a bit more expensive during the day than night

---- enough that it may actually work out more expensive overall o The meter is insufficient for the existing load

---- it could well be very old too - and miss-reading isn't unheard of

Economy 7 is typically favoured for storage heaters and such like.

You have 20 PCs & 4 Servers... o Hopefully distributed across more than 1 RCD

---- ie, RCBOs would be good here - Memshield look attractive (as RCBOs go :-) o Yes, earth leakage is relatively low per modern PC

---- however on 24 machines that could add up to sizeable total leakage

---- a 30ma RCD will trip at around 15-30ma

So the whole wiring installation beyond meter could do with checking, and usual check on Earth bonding for any office kitchen & services etc.

I prefer HVAC for people & a good heat removal system for the machine room, since 4 servers is hardly a particularly oversized load (unless they plan on more).

[tony sayer]

No wonder global warming is getting to be a problem. Are these the same people who'd object to a wind farm in their back yard too;?....

[Dave Liquorice]

But not by as much as one might expect. This 17" CRT consumes 60W, similar sized LCDs are 40 to 50W...

And probably make a bigger saving in the power consumption than switching displays to LCD... 6 x 40W to 6 x 9W, 186W saved or

1.5kWHr/8 hr day.

It might it depends on the night load obviously the more you use at night rate the more you save but to break even you don't need to use

*that* much at the night rate.

Based on (old) Norweb E7 and Domestic tarrifs with standing charges.

20 units at day rate requires 5.68 units at night rate to break even, thats a base night load of just over 800W.

On the same figures, once above 20 units/day total around 22% of that total needed to be used in the 7hr off peak period. 7hrs is 29% of the day...

[Steve Firth]

Switching to LCDs saved having to install uprated aircon at a call-handling centre where I do work on the network and software. I think you're blagging a bit here, since the 15" Trinitrons I use are rated at 240W and the 19" is rated at 350W. 40W for an LCD sounds about right.

Saving 200W/monitor is on line with the calculations for the call centre. 60W for your monitor sounds about right for standby.

[Dave Liquorice]

What the plate 100-240v AC

2.5A

So could be anywhere from 250W to 600W... Plugging the monitor via a little power monitor it takes 55W, OK it probably has a switched mode PSU which can confuse such power meters but looking at the UPS logs that indicates just over 100W, still somewhat short of the lower of the two figures above but admitedly more than 55W... The empirical "hand on box" would be nearer the 100W mark than 250W.

[Andrew Gabriel]

I measure monitors for AirCon loading, and they're nothing like the figures you have here. 20" monitors are just over 100W, and they scale down proportionally. You can get around 15% variation based on scan rate and image brightness too. Standby mode is typically maximum of 10W, although some have multi-stage standby and can go lower.

I haven't measured a flat panel display's power consumption so I can't comment on those. I could measure one when I get my true power meter back (currently loaned out).

[tony sayer]

I think that would be a good idea Andrew just to see how the relative efficiencies stack up.

I presume that your meter copes with switch mode power supplies OK?.....

[Sparks]

Okay, I checked it today and the maximum I saw on the meter (I didn't watch it all day!) was 58A I expect when the kettle, fridge, the three water coolers/heaters, all the lights and all the PC's are on this figure would be greater.

The Meter does state Max 40A

There doesn't seem to be any RCD's on the main (2) consumer units, just MCB's and a 100A isolator on each CU. There is a third very small CU with a main switch and two fuses, this is marked "Top Floor" No idea if this then connects to a newer CU or not - didn't get time to check! All the CU's connect to the meter via a Henley block

At lockup time, with most of the lights off, there was about 10A being consumed.

During the day I put my clamp meter around the main earth (the cable that comes from an earthing block where all the earths from the CU, Gas pipe, etc connect to, to the main incoming supply cable) This was showing between 800mA and 1A - should we evacuate the building!

Sparks...