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Topic Title: UPS power issue
Topic Summary: back up power supplies
Created On: 22 April 2013 11:15 AM
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 22 April 2013 11:15 AM
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jegm73

Posts: 1
Joined: 22 April 2013

Heelo

I work on UPS's and have electrical knowledge and have been asked a question which I'm sure i have the answer but would like it confirmed.

We have a load that peaks at 3.6kw the problem is that the customer wants it on a 13 amp plug - its multiple loads but the UPS has one input to the mains.

One solution was to use a double socket that feeds to the input, thus splitting the load over two 13amp fuses. The two plugs would be mounted together so to stop them being fed to differing sockets i.e potential phase difference.

Personally this seems in theory ok but I dont believe this is good practice and possibly would get flagged up.

Any comments please
 22 April 2013 11:23 AM
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broadgage

Posts: 1298
Joined: 07 August 2007

I would advise very strongly indeed against doing as proposed.

Single 13 amp plugs are intended for single appliances with a loading of 13 amps or less.
Two such plugs should never be connected together, there is a clear risk of fatal electric shock of someone touches the exposed pins of one plug whilst the other one is inserted into a live socket.

Also ring final circuits are not intended for the connection of single loads of more than 13 amps/3KW.

Install a proper socket, probably a "ceeform" type on its own circuit for the UPS.
 22 April 2013 01:26 PM
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joepostle

Posts: 49
Joined: 14 September 2011

I would agree with broadgage, a ceeform on its own radial. With the small UPS installations I have been involved with have all been supplied in this manner. Usually the customer is more satisfied with the slightly higher reliability of supply a dedicated supply, especially as being used to feed UPSs. Most of the UPS I have seen (desktop UPS aside) have 16a input connectors.

Along with the fact that ring circuits are only supposed to supply 13a loads there's also another factor of what else is connected to the ring and possible overloads.
 23 April 2013 03:11 PM
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AJJewsbury

Posts: 11502
Joined: 13 August 2003

Or if the load consists of a number of items of (IT?) equipment, split the load, use two separate UPSs and two 13A sockets. Bear in mind the limits of leakage currents allowed on a single 13A socket though - 3.5mA from memory.

Absolutely don't wire two plugs together - all to easy for one to be plugged into a 1-gang extension lead, or the end socket of a multi-way extension socket, leaving the exposed pins of the other live. (No apologies for the repetition)

- Andy.
 24 April 2013 01:40 PM
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joepostle

Posts: 49
Joined: 14 September 2011

That sounds like a plan. Cost aside the advantages of multi-UPS is extended battery times. Is also worthwhile reminding about replacing the battery pack(S) or UPS unit(s) every 3-5 years. I was called to a site a few years ago where conveniently there was a power failure and the connected load instantly lost power due to depleted batteries.

Having seen the symptoms first-hand I was able to advice for a replacement!
 24 April 2013 06:37 PM
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Avatar for OMS.
OMS

Posts: 19693
Joined: 23 March 2004

We have a load that peaks at 3.6kw the problem is that the customer wants it on a 13 amp plug - its multiple loads but the UPS has one input to the mains.


for how long is the peak - assuming the UPS itself can deliver this on the output side without dropping into bypass, the small peaky, short duration loads that go over 3kW won't have much of an effect on a 13A fuse anyway.

If the load profile is such that it sits substantially under 3kW and the excursion to 3.6kW is "short" then you don't have too much of a problem in reality.

Worthy of a note perhaps

Don't use two plug tops though - that's nuts

Regards

OMS

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