Consumer units -how do they work?

You need to know what is tripping out. I think that the rcd is generally right next to the big on off switch. The others will be current trips.

A 1kw motor may take a lot of current when it starts ac or universal dc which is what you have.

There can be several reason for the rcd to trip especially on brushed motors. Effectively they are detecting a miss match between the current going to the motor compared with what's coming back.

The insulation in the motor may be past it's best.

It might be full of dust including dust from the brushes. Sometimes this can be cured by stripping it and cleaning it very thoroughly.

These types of motors sometimes have suppressor capacitors built in. They can cause this sort of problem. So replace both with new ones or remove them. I didn't mention removing them.

I believe your rcd should be a 30ma type. In the early days much much lower values were often fitted.They caused all sorts of problems with lots of things. They are pretty simple things really. Maybe they can go wrong. Probably will if tripped frequently. They usually plug into the consumer unit so can be changed. I think some consumer units use a combined master switch and rcd. Those are likely to plug in as one unit as well. So will the current trips. None of this sort of stuff is intended to do it's thing very often.

John

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I am surprised you didn't then conveniently forget to pay them

I asked the OP if he had a capacitor start motor way back in this thread, and if he was running it off a B curve or C curve mcb, but didn't get an answer.

At my previous house I was running a single phase compressor with a 3hp motor and capacitor start, and these are notorious for tripping out B curve mcb's.

I put a C curve mcb in a spare way in the garage consumer unit myself, and took a direct feed via a switched outlet for the compressor off this.

Voila, no more tripping.

Edited By David Standing 1 on 06/01/2017 19:22:36

Edited By David Standing 1 on 06/01/2017 19:23:51

Umm... John, some of what you say is perhaps confusing. so.......

> I think that the rcd is generally right next to the big on off switch

actually, often in a modern consumer unit there are two RCDs. Often one at each end (or one at the end and one in the middle). On mine I only have one but it is the half way along the row

For the record, an RCD is generally easy to identify by the fact it has a test button and is double width. An RCBO has a test button but is normally single width.

> I believe your rcd should be a 30ma type. In the early days much much lower values were often fitted

I don't think I have ever seen an RCD with less that 30mA rating in a domestic consumer unit. Perhaps you are thinking of Voltage Operated Earth Leakage Circuit Breakers? They were a menace and I think the recommendation is to change them wherever they are found.

> Maybe they can go wrong. Probably will if tripped frequently.

They do go wrong and can be damaged if they trip when there is too high a current flow. They should be tested every 6 months using the test button and every 5 years using a proper tester. And replaced if they are known to have taken a full fault current. Not that either generally happens.....

> I think some consumer units use a combined master switch and rcd

Sometimes, but it is not common in the UK. I think (although I will stand corrected...) that RCDs do not meet the BS standard required for a main isolator switch. It is more common in garage consumer units where the RCD is not the main isolator (that is in the main board in the house).

I am assuming your reference to plug in units refers to the old plug ins that replace cartridge or wired fuses in the likes of MEMs or Wylex boards. I am not aware of any modern boards that use plug in breakers, assuming you don't count the crabtree starbreaker boards that have a plug in busbar connector.

hth. Toby

You forgot to mention that you also did a loop impedance test to check the C type will trip correct....

The OP said it's a dc motor David. Or universal. There may be capacitor in it but only for suppression.

If starting current is causing his problem the C curve might help.

It seems that garage CU's should only have on lighting and one power connection !

Vic If the electrician wont do it you could try pulling it out and fitting one yourself. It very probably will pull out just like wire fuse blocks do. We can change those ourselves - or at least replace the fuse.

John

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I have been sitting here expecting a comment/question from you .

John

As mentioned by Toby, the mcb's will probably be screwed to the CU busbar.

Oh, and another thing to mention (I think Toby might have done earlier) is that there is no standardisation with CU's and mcb's across different manufacturers, so a Wylex C curve mcb probably won't fit the cutouts in a Crabtree CU, and so on.

Edited By David Standing 1 on 06/01/2017 19:40:00

Thanks Toby. I'm surprised that they don't all plug in. I thought that all consumer units were like this one under the cover.

**LINK**

They tried rather low current rcd's in factories early on and I thought some also found their way into houses. Fridges and all sorts tripped them.

John

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John

The mcb's in the CU you linked are screwed to the busbar. You just can't see it, under the busbar cover at the bottom .

Posted by Nick_G on 06/01/2017 16:49:17:...... - Have you never been to the pub with a crowd of like minded guys.? Nick

Oh yes, forgot - will try it out with my mates down the pub tonight, although some of the group are power engineers who have little respect for the average electrician.
Just for the record - I didn't say anyone here is an average electrician.

I didn't want to disappoint

Posted by Clive India on 06/01/2017 19:54:29:

Posted by Nick_G on 06/01/2017 16:49:17:...... - Have you never been to the pub with a crowd of like minded guys.? Nick

Oh yes, forgot - will try it out with my mates down the pub tonight, although some of the group are power engineers who have little respect for the average electrician.
Just for the record - I didn't say anyone here is an average electrician.

Edited By Toby on 06/01/2017 20:23:05

Posted by Clive India on 06/01/2017 19:54:29:Just for the record - I didn't say anyone here is an average electrician.

Average electricians?

Like guys who sell up a small maintenance job into one which isn't actually required and involves much greater expense and then fail to conduct an adequate site survey and fit equipment suitable for the job?

Thanks for the (myriad) replies guys - didn't expect this one to run to three pages and counting! Not objecting at all though - an interesting read, and I've learned some stuff I didn't even ask about.

My original question was answered in the first few replies - thanks especially to Toby for a very clear and comprehensive answer at #3. I now know that it is an earth leak I'm looking for - it was the switch with the test button that tripped, so the RCD - I just wasn't sure about the difference between that and the MCB's.

The machine is a Record extractor manufactured in 1999. It's probably been sitting unused in a garage for years. Multimeter shows >40Mohms between live and earth with the power switch on and measured at the plug pins, but of course that's 1.5V DC so says nothing about a capacitative leak or higher voltage insulation breakdown. It's a brushed motor, so no start capacitor but a 1.0 microfarad supressor across the live/neutral terminals where the power cord enters. Then it goes to a mystery component (pic below), the power switch and finally the motor. If anyone can recognise the 'mystery component' from the crappy photo, I'd be interested to know.

Regards, Rob

Too small really but shows slight signs of being a filter for noise suppression. Some times just done with 2 capacitors.

John

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Agree with Ajohnw ...

Manufacturer's website is here: **LINK**

http://www.schaffner.com/index.php?id=44&tx_kesearch_pi1%5Bpage%5D=1&L=0&tx_kesearch_pi1%5Bsword%5D=mains+suppression+filter

You should find a direct replacement, or suitable equivalent at RS Components, or similar.

Note: This could well be the cause of your problem.

MichaelG.

As John says it looks like a filter Schaffner make filters and it looks like the diagram of a filter circuit in you picture although it is not too clear. Filters are often bad news when they meet RCDs. Try just running the fan without the filter, this may cause interference with other equipment so ok for a test but should not be used if it does interfere with other equipment.

Mike

I have zoomed in on the picture of the filter and I THINK I can see three capacitors. The one that is easily visible is between live and neutral this should not cause a problem. Of the other two which I think I can one will see will be between earth and neutral and the other between earth and live. On older filters these were normaly the same value. (I think about 0.1 uf) 0.1 uf has a reactance of about 32K ohms at 50 Hz so the reactive current through the one between live and earth will be 240/32000 = 7.5 mA This is not enough to trip a 30 mA RCD if there were 4 or more devices wil this type of filter the reactive current to earth would be enough to trip the RCD. We need to know the value of these capacitors to see if there value will cause a reactive current of 30 mA In modern filters this capacitor (If fitted) is a much lower value. Even if these capacitors don't cause enough reactive current to trip the RCD they can break down at a higher voltage so then need to be tested with an insulation tester which uses a higher voltage. DO NOT test them with more than 500 volts as it can destoy a good capacitor.

Les.

Presumably, Robin will have sight of the actual item, and can [hopefully] identify the part number and schematic.

MichaelG.