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Trip Switch

Community Veteran
Posts: 1,236
Registered: 02-08-2007

Trip Switch

I am always adding bits to my home network to feed my facination with networks and cabling. Recently I added a power meter to the whole thing to see how much power it was using before then adding a ups. That all worked fine.
With everything switched on I am drawing about 400 Watts (just under 2.5 amps) according to the power meter. I have the whole thing connected to a spur that I wired into the socket ring in the house. As the wiring in my house is quite old and still using fuses I decided to add a small consumer unit to the spur with a 6 amp trip. At this point I will let you see exactly what I am talking about. The first picture on the following page shows everything:
http://www.seanbranagh.com/network
When I simulate a power failure the UPS takes over as it should and runs everything for about 10 minutes which is fine because most of the power failures I have had recently have only lasted several several seconds but long enough to reboot my servers and router. For short failures such as this the system works perfectly. The problem is when the power fails long enough for the ups to cut out. When the power comes back on the ups turns everything on with a relay inside. The resulting spike causes the trip switch to go off. When I first realised the problem I changed the trip from a B type to a C type as I knew from previous experience that the C type were less sensitive. This did not cure the problem. Any ideas?
If I change to a larger trip maybe 10 or 16 amp will the spike still cause it to go off?
8 REPLIES
VileReynard
Seasoned Pro
Posts: 10,978
Thanks: 265
Fixes: 11
Registered: 01-09-2007

Re: Trip Switch

Why have a trip switch?
A fuse can take short power surges - before blowing. So wouldn't a standard 13A fuse do the job?

minkey
Grafter
Posts: 386
Registered: 22-07-2007

Re: Trip Switch

Have you measured the wattage of the UPS kicking back in? It may be more than the 6A fuse can cope with, maybe increasing the trip amperage would cure it.
Jeff
Community Veteran
Posts: 1,236
Registered: 02-08-2007

Re: Trip Switch

I do already have a 5amp fuse in the plug but I just wanted the consumer unit cos I like having lots of stuff like that on the wall like the picture shows. Now that it is there I need to resolve the issue.
The spike is imposible to measure with the power meter as it only lasts probably milliseconds. I would also imagine it to be several hundred amps which is why I don't think a larger trip will solve the problem but I am going to try a 10 and 16 amp anyway. Lets hope for the best.
alanb
Grafter
Posts: 459
Registered: 24-05-2007

Re: Trip Switch

An experienced electrician (which I am not, by the way,) would tell you that circuit breaker fuses are very prone to 'nuisance tripping'. If you can't prevent spikes, the usual solution is to replace the circuit breaker with an old style cartridge fuse, which will react a little more slowly.
I rather suspect you've got a UPS that operates in two mutually exclusive modes, it can either supply power to your equipment from a battery, or it can supply power directly from the mains. During switchover, it's going to cause all the switch-mode power supplies in you equipment to play havoc with the mains waveform.
The best UPS equipment always supplies power from the battery, while keeping the battery charge topped up from the mains, so no switching is required. The equipment always gets clean power, and there is less distortion of the mains supply because better power-factor correction can be designed in. This type of kit is a bit more expensive though, and running costs are higher because you have to replace batteries more often.
Incidentally, a 6 amp circuit breaker fuse is normally used for 5 amp lighting circuits and would be used instead of a 5 amp cartridge fuse. The slightly higher current rating of the breaker is intended to help compensate for its much higher sensitivity, so it is possible that replacing it with a breaker with a higher current rating will solve your problem - it just depends on how bad the power spike is.
Community Veteran
Posts: 1,236
Registered: 02-08-2007

Re: Trip Switch

I have cartridge fuses in my main fuse box as I mentioned earlier. The reason I want a trip is because I have seen first hand in the past how much it takes to blow a cartridge fuse and it is quite a bang and possibly even a fire.
Like you said the problem may be solved with a larger trip. I will know on Monday when I buy a few different sizes. They are only £2 each.
As for an online UPS, I would love one but they do, like you said, cost a bit and more than I am willing to spend on this project.
PunKrocker
Grafter
Posts: 103
Registered: 06-11-2007

Re: Trip Switch

Quote from: seanbranagh
If I change to a larger trip maybe 10 or 16 amp will the spike still cause it to go off?

Can you not measure it with a DMM or similar?
VileReynard
Seasoned Pro
Posts: 10,978
Thanks: 265
Fixes: 11
Registered: 01-09-2007

Re: Trip Switch

Quote from: seanbranagh
...I don't think a larger trip will solve the problem but I am going to try a 10 and 16 amp anyway. Lets hope for the best.

If you have a 16A trip then it's going to be a bit tough on the old ring main isn't it? You'd better invest in some extra thick copper wiring.
Don't be scared of 13A fuses making a bang. I was once installing an electric cooker - but with the mains power still on. I accidentally allowed the live and neutral wires to touch. A 30A fuse makes quite a loud noise - but not exactly in the Guy Fawkes category.

alanb
Grafter
Posts: 459
Registered: 24-05-2007

Re: Trip Switch

Sean,
there's no reason why a cartridge fuse should be a greater fire risk if it is installed correctly in equipment that complies with regulations. If a fuse itself was faulty in some way (a manufacturing fault, for example) it could conceivably be a fire risk, but you cannot conclude that a circuit breaker fuse would be less of a risk in such circumstances.
Bear in mind that the primary purpose of fuses in consumer units is to protect the house circuits from damage due overload. If you've used the correct type of cable for the spur from the ring main, and if the ring main meets modern regulations (i.e. 30 amp capacity) then the spur is rated for 15 amps. An appropriate fuse is therefore a 15 amp cartridge or a 16 amp CB. Your computer equipment will be protected individually, if required, either by fuses in 13 amp plugs or internal fuses in psu's, etc. so it doesn't make sense to get too hung up on the lowest possible value for the CB in your consumer unit.
Of course, if this consumer unit is just for show, as you seem to be implying, then you could just bypass it, and it will still serve the required purpose.  Undecided (That's not a serious suggestion by the way, though I believe that there is no requirement to include a fuse in a spur from a ring main.) I think an RCD type earth leakage detector could be more useful in your application, as a backup to the protection built into individual items of computer equipment. You can buy RCD breakers that fit into a modern consumer unit.

Axis,
16 amps shouldn't be too tough on a ring main. Domestic ring mains are normally wired with 2.5 mm sq cable that has a maximum current rating of 20 amps. As it is wired in a ring, the maximum current capcity of the ring main is 40 amps, and it would normally be fitted with a 30 amp fuse or 32 amp circuit breaker.