Earth Leakage

[lemmy1234]

All,
Having discussed this with a number of colleagues of mine - we are no closer to finding a definative answer.

On a regular basis we are involved in the procurement of various electrical distribution equipment, with the majority of work being involved with LV Final Distribution (MCC Feeds to Distribution Boards, Motors and Heaters)
On most occasions we are offered equipment with Earth Leakage protection - as specified by vendors.

I feel uncomfortable leaving this in the hands of "others" BUT cannot find guidance on Earth Leakage Protection setting. Having the various options of 30mA to 300mA leaves room for considerable error for personal protection etc.

Can you advise?

 

[ScottyUK]

First question is what country are you in? Local codes usually contain requirements for personnel protection. In the UK, for example, earth leakage detection for personnel protection requires 30mA instantaneous trip, with 10mA instantaneous being required in higher risk areas. For earth leakage protection a trip at 300mA with a time delay may be acceptable to meet fault clearance times and to ensure coordination with downstream devices, but is not acceptable for personnel protection. You really need to seek help from the design engineer for the project.


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If we learn from our mistakes I'm getting a great education!

 

[lemmy1234]

Scotty,
Thanks for the reply - i am more than happy that with equipment that may involve contact with operators and live maintenance etc requires 30mA (or less) as a standard.
(I am in the UK also)

But when equipment such as motors and heaters are being offered from manufacturers with differing EL Protection sizes and settings - things become a little blurred.

I would have expected (and there may be one) but i cannot find guidance documents (BS/EN/IEEE Standards) on specifying and setting of EL Protection for equipment at various ratings.

I was hoping for a procedure for calculating EL from equipment rating or FLC.

The standard reply i get within this office when querying this is "ask the motor/heater vendor" and "turn it up if it trips on start"


Not - i think you will agree - the engineering way

Thanks in advance

 

[burnt2x]

lemmy1234,
So you need answers the engineering way!
IMO, Earth leakage on electrical equipment should be limited below the withstand capability of the equipment against such events. The higher the earth leakage setting of the ELR, or the longer the leakage current is permitted to continue to flow, the more damage to the equipment. Having said that, you need to know how much energy the equipment can withstand without damage? This energy is normally measured in kW-cycles (which can be converted kW-sec = energy). If my memory serves me well, the maximum energy that an equipment can survive is 20,000 kW-cycles! Dividing the withstand capability by your equipment voltage will give you ampere-cycles(or amp-sec). How long you intend for the fault to flow will then determine what the level/setting of your EL will be (amp-sec /sec = amp).