Electrical help

Wyrdo · 18 Feb 2006 at 15:47

Quick question for anyone who knows about this sort of thing.

I have a dehumidifier upstairs and it's now on it's 3rd fuse in the plug (5 amp) it's been running fine for a week but the last 3 nights it's blown the fuse.

Any ideas?

Stringy · 18 Feb 2006 at 15:48

If that's the fuse that it's meant to need then it could be faulty. I wouldn't use it.

lordedmond · 18 Feb 2006 at 16:11

that fuse sound a bit light for a dehum , they have a fridge compressor in they ant the start up currents can be quite high,

check the manual, but i would try a 10 amp fuse if it blows that then there is sumut up

Wyrdo · 18 Feb 2006 at 16:17

It came with a 5amp, I was just wondering if that was too low though. If it goes again I'll try a bigger fuse.

LordSplodge · 18 Feb 2006 at 16:22

Just remember - electrcity kills. Don't mess, if the manual says it needs 5A then it's bust.

Fallen Hero · 18 Feb 2006 at 16:31

Could also be the unit at fault?

singist · 18 Feb 2006 at 16:46

As a rough guide ....... divide the wattage by your voltage and it'll give you a good idea of the fuse to use ie if it's 1000 watts (1kw) then divide by 250 (volts) and get 4amp .....I'd go with 5amp fuse, in this instance.

If it's got the correct fuse and keeps blowing, something wrong, get a pro to fix or bin it. Do not start putting much bigger fuses in (13 amp) etc the fuse is there for your safety.

lordedmond · 18 Feb 2006 at 16:55

singist said:
As a rough guide ....... divide the wattage by your voltage and it'll give you a good idea of the fuse to use ie if it's 1000 watts (1kw) then divide by 250 (volts) and get 4amp .....I'd go with 5amp fuse, in this instance.

If it's got the correct fuse and keeps blowing, something wrong, get a pro to fix or bin it. Do not start putting much bigger fuses in (13 amp) etc the fuse is there for your safety.

your calculation is correct however with an inductive load ie a transformer or electric motor ( a compressor is under full load at start up ) the inrush current is many time the normal running current, hence the problem in correctly fusing such items

thats why i recomended a 10 not all the way to a 13

btw it takes about 2500amp to blow a 13 amp fuse ( that what the scope will tell you the peak instananious current on a dead short is very high indeed )

clockworks · 18 Feb 2006 at 18:18

Does the room get cold at night?

Dehumidifiers are prone to icing up in a cold, damp, room. Some models have a de-icing heater, some will cut out, and some will just keep going until the fuse blows!

Shifter_Hull · 18 Feb 2006 at 19:43

so 230 volts/5amp
its using 46 watts of power on a normal mains supply that should be fine
if its breaking fuse the unit may have a bad earth or a fault do not upgrade the fuse

LoadsaMoney · 18 Feb 2006 at 21:01

AMPretty sure it will be the unit if it keeps blowing the fuse, i would'nt use anymore if it blows the current one, thats just my opinion for watt its worth.

benjo plz. · 18 Feb 2006 at 21:03

Sounds like the unit. It should have power usage info on it somewhere and will say the max fuse rating.

Adam_151 · 18 Feb 2006 at 21:29

lordedmond said:
btw it takes about 2500amp to blow a 13 amp fuse ( that what the scope will tell you the peak instananious current on a dead short is very high indeed )

It depends how quick you want to blow it, you'd need a pretty low impedance supply to get that much to flow*, but if you did, it'd be all over in half a millisecond, 90A is what you need to open it in 0.4 seconds

*I suppose if you were not too far from the local transformer and the socket was pretty near to the supply intake...

@OP, is the fuse rateing marked on the unit, if not tell me what size cable is on it, and the length of it and I'll tell you what the IEE code of practice for servicing of portable appliances says

as has already been said can't just use watts law here, the start up surge of motors can be quite high

Mr. Brightside · 18 Feb 2006 at 22:24

*Don't really know much about fuses so I may be entirely wrong*

But I heard there are quick-blow fuses and non-quick-blow fuses. Is it a possibility that it is designed for non-quick-blow (due to the large inrush of compressor), but that you replaced it with a quick-blow? That could explain why it keeps blowing but then the question still exists of why it blew the original. And I thought 'normal' fuses are of the non-fast-blow kind so you would have to have specifically got fast-blow?

Probably wrong lol but thought I may aswell offer it

Scream · 19 Feb 2006 at 00:10

If you buy a unit and its fitted with a 5amp fuse, leave it with a 5amp fuse when needed replacing.

The fuse will only blow if the unit is trying to pull more than 5A. It doesn't matter if the unit requires more power at startup etc for the unit should have been designed with that in account.

The simple fact is, the unit wants more jiuce than it should be allowed. There's nothing you can do apart from change the fuse each time but from the signs of things, the unit is faulty or on its way out.

It's not an earth leakage fault because most homes now have RCD protection on the circuit so it would trip the RCD.

If your house for some reason isn't RCD protected, you could get an RCD plugin adapter which would tell you if its an earth leakage fault.

My advice would be, if it was new, send it back and get a replacement. If it still occurs, get a different brand.

Adam_151 · 19 Feb 2006 at 01:06

Scream said:
The fuse will only blow if the unit is trying to pull more than 5A. It doesn't matter if the unit requires more power at startup etc for the unit should have been designed with that in account.

It should be noted that its normal for reactive loads (and even some resistive ones) to exceed the fuse rating momentalily on start up, for example the power supply in in your computer might pull 60A + for a very short duration as the capacitors charge up, I would say 5A might be pushing it a little, have a look to see if it recommends a fuse rating on the information plate, if not provided the cable is 0.75mm² CSA or greater and no more than 2m then put a 13A in

(the plugs and sockets regulations requires that in the absense of a makers recommended fuse rating on the device, then the fuse can be sized in accordance with BS1363)

Before people start calling me a dangerous fool... the same appliance is most likely sold in europe where there is no such thing as a fused plug, all appliances are protected by a C16 breaker or a 16A fuse at the distrubution board protecting the radial circuit, the reason we have fused plugs is because of our penchant for 32A ring mains in this country (something that wouldn't be permitted anywhere else)

Adam_151 · 19 Feb 2006 at 01:08

null said:
*Don't really know much about fuses so I may be entirely wrong*

But I heard there are quick-blow fuses and non-quick-blow fuses. Is it a possibility that it is designed for non-quick-blow (due to the large inrush of compressor), but that you replaced it with a quick-blow? That could explain why it keeps blowing but then the question still exists of why it blew the original. And I thought 'normal' fuses are of the non-fast-blow kind so you would have to have specifically got fast-blow?

Probably wrong lol but thought I may aswell offer it

You do indeed get quick and slow blow fuses, BS1362 fuses (plug top fuses) however are only available in one 'flavour'

cootuk · 19 Feb 2006 at 01:43

We had an Ebac once with a dusty sensor and every so often it kept cutting on and off rapidly - which blew the fuse. Hoovering out all the innards, especially around the control boards cured the rapid cycling.

Mickey_D · 19 Feb 2006 at 03:21

Shifter_Hull said:
so 230 volts/5amp
its using 46 watts of power on a normal mains supply that should be fine
if its breaking fuse the unit may have a bad earth or a fault do not upgrade the fuse

Volts TIMES Amps = Wattage

Wattage DIVIDED by Amps = Voltage

Therefor 230 Volts on a 5 Amp draw = 1150 Watts

lordedmond · 19 Feb 2006 at 08:09

Adam 151

I bet the letters PAT mean something to you then