phase to earth fault
- Thread starter spydaweb
- Start date
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possible outcome: fire. altho in a properly designed circuit, the overload protection should disconnect the supply before this has time to happen.
if it was RCD protected, the RCD would trip at 30mA (or whateva its designed to trip at). and a low resistance between phase and earth would not go unnoticed. since there would probably be either a fire or no power.
if it was RCD protected, the RCD would trip at 30mA (or whateva its designed to trip at). and a low resistance between phase and earth would not go unnoticed. since there would probably be either a fire or no power.
thank for that
this is what i thought but i got this question from college
a low resistance phase to earth fault occurs in a lumiair. state the possible out come if this went undetected.
the value of the low resistance is 100 ohms explain what effect this would have on the overcurrent device.
i answered basiclly what you put but guidance note say that overcurrent device may not trip as currnt to low. how ever i thought lower resistace = higher current. please can you clarify this?
this is what i thought but i got this question from college
a low resistance phase to earth fault occurs in a lumiair. state the possible out come if this went undetected.
the value of the low resistance is 100 ohms explain what effect this would have on the overcurrent device.
i answered basiclly what you put but guidance note say that overcurrent device may not trip as currnt to low. how ever i thought lower resistace = higher current. please can you clarify this?
Surely you can cope with Ohm's Law?
Work out the current that would flow through a 100ohm resistor with 230V across it?
Work out the minimum resistance that would cause insufficient current to flow to trip a 6A Type B in 5s?
Work out the current that would flow through a 100ohm resistor with 230V across it?
Work out the minimum resistance that would cause insufficient current to flow to trip a 6A Type B in 5s?
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100 ohm load wouls be something like a 500W floodlight. Generally adding one of these to a lighting circuit would not cause it to trip and would not overload the cabling. But whatever the load is, it must either get rid of 500w somehow, or just get hotter and hotter and hotter...
spydaweb said:what is the possible out come of a low resistance phase to earth fault that goes undetected?
and how would a value of 100 ohms affect the over current device
100 ohms is NOT a low resistance in electrical terms
its a resistance in that very very nasty band which is too high to trip the breaker but which is low enough to produce significant heat when mains voltage is applied to it.
as has been said it will be a load of about 500W so thats about the same heat output as your garage floodlight. that amount of heat in a situation where its not expected has a significant chance of melting equipment or starting fire. (floodlights and heaters are EXPECTED to get hot and are designed very very carefully with this in mind)
thank for your replys
the answers you gave were basiclly what i had answered but had it returned marked wrong. maybe i worded it wrong. i will resubmit it in a different form and see what happens.
i am a 1st yr adult student retraining and still trying to come to grips with all these new phrases and mathmatics so thanks for your patiants
the answers you gave were basiclly what i had answered but had it returned marked wrong. maybe i worded it wrong. i will resubmit it in a different form and see what happens.
i am a 1st yr adult student retraining and still trying to come to grips with all these new phrases and mathmatics so thanks for your patiants
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