RE: [CAD_CAM_EDM_DRO] ELCB Issues

Hi Lester and Ian

As Lester say the cause is an Earth fault, but it is easy to get some
confusion here, so first you must consider how the ELCB works.

It does not detect current in the Earth wire, it looks at the live and
neutral, the current travelling in each should be the same, if some is
leaking to earth then live and neutral will be imbalanced and the trip will
go.

So you have to be looking for something, insulation failing probably between
Live and Earth, or perhaps a short occurring between Neutral and Earth.

Like Lester I have found loads of problems with USA kit, and lots of stuff
that would never come near their UL safety specs.



Things to look for.

Failed Suppression capacitors on motors filters and the like. These will
often be wired in a Y with a cap between the phases, and one from each phase
to earth, a failure here and the ELCB will go. In the UK we use special
capacitors that fail short circuit, or open circuit, but others seem to just
use a hi voltage cap.



Insulation in the motor, hopefully it will be a chaffed wire, or spur on the
terminals.



VFD's will dump enormous energy on power up, all you can do for these is put
a separate supply in for the machine with an ELCB rated to allow a higher
earth current.

Some motors while they have good insulation have enough capacitance between
the windings and earth to trip an ELCB, again a high rated ELCB is required.



If you use a high rated ELCB (really lower rated in terms of safety), only
use it as a supply for the machine, and only do this if you are sure there
is no fault and have tested the insulation resistance with a proper
insulation tester, 600V test should be OK though I normally check at 1KV and
higher. Remember this supply is no longer as safe, whilst you wouldn't want
to do it, you can stick your finger in the mains on most ELCB house supplies
ans it will trip before anything nasty happens, you just get a joult. On my
mill for the VFD I had to up the trip current to 750mA, this provides very
little protection, fingers in there and it will kill, so every thing is
double insulated just in case, about the only protection it gives is to shut
the supply off if the wires catch on fire.

There are also certain legal issues if you change the ELCB supply now in the
UK under Part P of building regs. Many people ignore this, but you should be
aware and if in any doubt at all, safety is the issue, the law I feel is
second to that, and if you have any doubts seek professional help.





Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Lester Caine
Sent: 18 March 2007 08:34
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] ELCB Issues



xj5373 wrote:

> Hi,
> I have stripped out the old control system from a Denford Easimill and
> replaced with Mach3 via a Bob Campbell break out board. It works
> beautifully but from the start I had a problem with the machine
> dropping out the ELCB on the mains supply. The machine is plugged into
> a ring main which is fed via an earth leakage circuit breaker from our
> consumer unit (I should say that I am in the UK). I found that if I
> Estopped Mach3, this drops a relay connected to the change pump which
> takes the power off the stepper power supply. Giving it a minute or two
> allowed me to isolate the machine from the mains without the ELCB
> dropping.....more often than not. Isolating immedaitely after Estop
> seemed more likely to drop the ELCB. I have opeated this way since last
> summer but just now I can't reset without losing the ELCB. I have the
> machine powered up but in Estop mode, pressing reset powers the relay
> via the charge pump output of the break out board which switches 240V
> onto the stepper power supply and the inverter which is controling
> spindle speed.
> I know what the ELCB does but what is it that is tripping it? Any help
> or hints greatly appreciated.

The only thing that will trip the ELCB is an earth fault. So there must be
something giving feedback into the protective earth. The first thing I would

be looking at is what is connected to that earth. I don't like the mains
arrangements on any of the American boards I've seen and none of them pass
the
European creepage and clearance rules. Which need to be need to be a good 2
times that needed for 110V ;) So I tend to stick to external mains
components
such as solid state relays and just run DC from the boards. Then you can
ensure clean live and neutral connections.

--
Lester Caine - G8HFL
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