Re: Choosing Consumer Units

I have a 2.5HP cyclone type and that is specified as requiring a type > C breaker.

Certainly, if the equipment specifies A 32A Type C, then Type C it is. However, if they specify Type C @ 10A, say, (for a 2kW machine), then a 32A Type B will actually have more resistance to switch on surges than that. Of course, you'd also have to ensure that a 13A FCU/plug top fuse provides enough overload protection.

Christian.

Reply to
Christian McArdle
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The reason I even know about type C MCB's is because one or two people on a woodworking forum suggested that I may want type 'C' to cope with large start-up current draining for things like the vacuum system and some large machinery which doesn't have a 'soft-start' feature.

Some have suggested (they are not electicians) that I may see 4-6 times normal current useage on startup for some machinery. Does this sound right?

Is it possible to measure the peak current during startup of my tools somehow, to see if I'd need a type C? or should I just fit type B's and change them to type C's if I keep tripping them?

Regards, Mark

Reply to
Mark McGee

4-6 times wouldn't be a problem. A Type B is guaranteed to allow 3x current briefly. This is for the full 32A. So you would have to draw 96A to get a chance of instantaneous disconnection. A 1800W (7.5A) vacuum would have to draw over 12 times its rated current to trip the 32A Type B. Of course, if it has its own dedicated 10A circuit, a Type B is allowed to trip at only 30A, which is only four times its rated current, which becomes much more of a likely event. Also, if you are likely to start both machines at precisely the same time with no stagger, then a trip becomes a possibility, as you are then talking about a 15A "appliance", giving only a 6.4 times surge to possibly trip. This can drop to 5.3 times if other power hungry appliances are in use on the circuit.

Well, MCBs are as cheap as chips. I'd buy both types and keep the Type C in reserve and swap it over if it really does trip the Type B.

Christian.

Reply to
Christian McArdle

It could be.

I would ask the manufacturer what is required.

.andy

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Reply to
Andy Hall

I'm gradually homing in on a design here. But I do need a bit more of your help.

I think the home consumer unit is sussed - I'm getting a MK sentry split load with RCD (30mA) and 100A switch.

From the Home CU, I will run about 120ft (~50 metres) 10mm 3-core SWA to the workshop.

Q1. Should an isolator switch for the workshop be at home, or in the workshop? Q2. I think I should run all circuits EXCEPT lighting behind an RCD? Individual RCD's and RCBO's (for MK Sentry at least) seem prohibitively expensive. Any recommended kit or setup for this?

Also, from the home CU, I will run 6.5mm cable to an outbuilding (old coal shed), where I will run a few sockets, 2 ordinary light bulbs, a halogen light, a halogen security light, and some low voltage uplighters. I imagine 4 circuits for this.

Q3. I assume for this CU, I should run EVERYTHING behind an RCD? Q4. Isolator switch? Where - indoors? in the outbuildings?

Many thanks Mark

Reply to
Mark McGee

On 2 Apr 2004 08:35:56 -0800, in uk.d-i-y snipped-for-privacy@csfb.com (Mark McGee) strung together this:

Both. There should be a DP isolator in the house for the workshop circuit and also an isolator in the workshop. This one will be the main switch of the CU in the workshop.

That's your only 2 options really, RCD and individual MCBs or RCBOs for each circuit. The way you suggest is fine, RCD to all sockets and machinery and no RCD for the lights. The only thing I will say is, and I seem to recall you said about a freezer in the workshop, don't put the freezer socket on an RCD. Run it on a 16A radial on the non-RCD side.

That would be 6mm then. ;-)

I would just put the sockets an the RCD.

As the workshop, one at each end.

Not a problem.

Reply to
Lurch

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