OT - Advice from sparky needed
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The 40A / 30ma RCCD in my workshop keeps tripping when my milling machine is on, no doubt the 30 year old motors have some small earth leakage. How can I get around this problem? How dodgy is it to replace the RCCD with 100ma or just a normal over current breaker?

Team Racing

If it were me and You have the space, I'd come off the incoming side from the main board, and put a separate small board in (just a 2 gang) and put a normal rcb in it to the current rating of the mill, making it it's own dedicated supply.

They say it only takes 50mA to kill you, thats why most consumer units are fitted with the 30mA RCCD.

Its up to you if you want to up it.

What the mind can conceive the mini can achieve
MITP 2012 17.01 seconds 1/4 mile against "The Don"
MITP 2013 16.83 seconds 1/4 mile

Jim, you are using a phase inverter, the motor s on the mill are not directly coupled to the mains supply are they?

Its sort of a voltage transformer, and in my experience transformers can and do trip RCD's without there being a fault. You could check the motors with a multimeter, but ideally you need a Megger to test the insulation of the motors. That said, are the motors not DC, or are there a mix of AC and DC?

i had the same problem with the flowbench motor jim . I was using a vfd, and apparently these shoot a bit of dc down the return which reads as an imbalance on the rcb and trips it .

my solution was to take a feed previous to the rcd ,and run the bench on that . bingo, no trippin' man !

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

As Robert says, run a dedicated non RCD supply just for that machine and make sure it has a good earth. Just don't get looping any sockets off it for anything else!

I'll do as Robert suggests, I'm using a rotary phase converter and a VFD so that would explain the issues.

Cheers Guys, looking forward to machining my first parts this afternoon, G code ready :)

Team Racing

This is getting more odd. Coming out of my mains supply meter I have two pairs of 16mm2 cable. One set goes to my house consumer unit, and the other out to my workshop.

I've now connected my mill to before the Rccd in the workshop.
now when I run the mill, after about 30 secs it trips the RCCD in the house (which it's not connected though). Any ideas?

Team Racing

Having covered it in first aid and electronics and EEP 30ma can kill you, as low as 26ma has been known to stop a heart of an unhealthy person

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Any ideas how I can work out where in the machine the fault is? With the main spindle
motor not running I still get same issue.

Team Racing

Its all very well taking rcd's out of the way for one circuit blah blah ect ect-but to comply with the regs its only ok if the earth fault loop impedance(Zs)for that circuit is low enough-or if your on a TT system a) the zs will more than certainly be too high and b)there will most likely be one big rccd protecting the main incomer-if this is the case either way, to keep it safe and in the regs your fucked.

Don't suppose you could post up/pm me a picture of your main incomer and where is splits to the garage, I may be able to offer some help. For the record its less likely to be the machine as ac motor drivers/inverters are something that has been totally overlooked with the new regs and they can give these issues due to the reasons stated by Robert but I have seen many of the smaller electronic only drives running on rcds without issues, not too sure on rotary converter issues tbh.

Edited by oli79 on 29th Nov, 2013.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

If indeed there was a link/cross between the two rcds then they would trip as soon any meaning full load was pulled from any circuit connected to them- ie more than 30 ma,in reality if that condition existed you would most likely have a job on even getting the rcd to stay in.

In this case now the rcd protection in the garage has been removed the most likely reason the house rcd trips even though it is upstream of the garage circuit is the dc that's fed back into the earth.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Can you get hold of a continuity tester or borrow one? It will allow you to narrow down the area at fault, just make sure no computers are connected as they don't like the test .

You could ask your local collwge if they would be interested in on the job training, may take a few weeks to do though as they require a risk assesment to be done but some will do it.

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Paul-the test you refer to is an insulation resistance test used to prove any leakage faults live-earth or neutral-earth and would only be of use on the motors in this case.

a continuity tester in the terms of domestic electrical use is used to measure the resistances of fixed wiring earth cables which in turn is used to determine the zs for each circuit, the importance if which I mentioned above.

Either way its going to tell you fuck all, the motors are not connected directly to the mains supply- the drive/ inverter is, my issue is my real world knowledge of rotary phase converters is very limited but I have heard it disscussed before by others also in the trade that the dc feedback they provide can cause rcd issues

Edited by oli79 on 30th Nov, 2013.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Thanks for all the input guys, I'll grab a photo and upload today

Team Racing

one of my chaps on the flowbench forum wrote this jim ..


''It is quite likely, that in order to make the VFD pass the ever more stringent European conducted noise emmissions tests, some pretty serious capacitors have been fitted within either the VFD itself, or it's associated black box filter, between the mains wiring and ground wire.
That will make yor VFD very green and environmentally friendly, but your ground leakage current will probably now be high enough to trip the earth leakage detector.

Try connecting the mains straight to the VFD, and toss the external black box noise filter.
See if that solves the problem. It may, or may not, but well worth a quick try.

Removing the earth wire from the VFD will fix it for sure.
As long as you ground any exposed metal parts that could become alive, such as the frame of the motor, and metal body of the speed control potentiometer, it bypasses the bullshit, while still providing full electrical safety''


in case its of any help.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

That is the test I ment, and I thought he was after finding the leakage? Which was causing the problem, it can be used on cpc and any other wires so long as its not sensitive, so start button, safety stops ect can still be checked not just the motor, it will prove if it is the cpc/earth causing the problem or if it is line or natural shorting as well.

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Paul- insulation resistance testers / meggers are for testing fixed wiring not machines/ appliances. In fact the only other thing I would dream of using it in would actually be the motor itself-nothing wrong with that, what you state about trying to locate the leakage is spot on, what I'm saying is these are not motors connected directly to the mains- there are vfm drives and a rotary phase converter in between

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Roberts hit the nail on the head with a most probable cause and the solution,this is also what I have heard this from other sources during my time at work, all that concerns me is that Jims existing installation is capable of safely providing a non rcd protected supply, he is emailing me a pic, I will try my best to help.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?