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single earth leakage detection for several 'clients' ?

Hi,

earth leakage detection device = ground fault circuit interruptor protection device. I'm on 220V AC.

The old office building where I'm located has recently started installing one earth leakage detection device for several users.

As expected, when someone brings in a 'leaky' device, all users on the circuit are punished ! I moved my computer on to the light circuit which seldom loses power.

It seems to me that domestic usage of earth leakage detection doesn't apply to 'commercial'/office block usage ?

For domestic:

  • the owner knows and controls all the devices,
  • the 30 mA is probably based on an average fatal dosage ?
  • they assume that the rest of the 'devices' total to < 10 mA ?

So what if the circuit has already got several devices whit a total leakage accumulate to 25 mA. And even if 6 mA is not consdered a problem, you still get a power-out for all the clients !

It seems to me that you need a 'delta' [rate of change] measurement of the imbalance of the live and neutral currents. It's realistic to assume that not 2 or more outlets will develop a fault at the same time [except at initial power-up]. So if XmA is the critical/dangerous current, even if the total leakage has accumulated to say 5X mA, a further change of +0.5X mA doesn't justify a power-down.

Do such devices exist ? I read via google 'self tuning' earth leakage detection devices; what is that ? What is the proper method, when say 10 offices are on one switchboard ?

Thanks for any info.

== Chris Glur.

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Helps to say which country too so we know which regulations apply. My response is based on UK regs, which may be quite different from your local regs, although it sounds like some aspects of circuit design might be similar.

Do you know why? e.g. Protection against electrocution; Protection against high earth fault loop impedance; Some regulation change.

Do any of these GFCI's protect more than one circuit, or are different users sharing the same circuit?

Yes. The trip current might be lower -- a 30mA device must not trip with 15mA leakage, but must trip with 30mA leakage. So it would be within spec for it to trip at just 16mA.

Do you know the devices installed are in fact 30mA trip rating?

Actually the circuit design leakage should not exceed 25% of the device's trip rating, i.e. 7.5mA for a 30mA trip. Each piece of class I earthed IT equipment can leak up to 0.75mA through its RFI supression components, so a 30mA protected circuit should not be designed to feed more than 10 of them, i.e. 5 PC's and 5 monitors. (In the UK, a circuit designed for even 7.5mA leakage would require high integrity earthing.)

You are trying to design a device to solve the wrong problem. I suspect the GFCI's have been inappropriately installed in your location.

Circuits feeding non-portable IT equipment would not normally require GFCI protection against electrocution. They might need GFCI protection against high earth loop impedance, but that would normally be 100mA minimum, and possibly with 200mS time delay too.

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Andrew Gabriel

A correctly wired device should have no leakage to the safety ground. Even if 6mA is below the trip limit, it shouldn't be there. The GFCI devices are probably doing their job. Perhaps the installer knew about your officemates preference for using defective equipment.

Do you disagree? What kinds of equipment would you expect safety ground current flow and why would that be acceptable?

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