UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

philthespark · 14th Apr 2018, 9:23 pm

In the London area, earth loop impedances are quite often lower than the rest of the UK due to the larger numbers of substations, most MCB's in a domestic scenario are rated at 6 thousand amps withstand, however, there are some 10,000 amp ones available. Although a breaker may be rated at say, 32A, in the time it takes to trip, you can get massive currents flowing, potentially in the order of a few thousand amps, enough to do major damage! one important thing to remember, never open a switch or breaker on a fault, if you are ever unfortunate enough to close one and then realise there's a problem, DO NOT try and open it, let the fuse/breaker clear the fault,there are more injuries caused by attempting to open a circuit under fault than there are closing one. We were always taught the "left hand rule", if the handle on the unit was on the right, then operate it with the left hand, that way your body is to the right, and not in front of the unit, very handy if anything happens to go wrong, especially if the circuit is a few hundred amps.

14th Apr 2018, 9:23 pm	#43
philthespark Pentode Join Date: Oct 2017 Location: Newton-le-Willows, Merseyside, UK. Posts: 158	Re: Source impedance of mains, a workaround? In the London area, earth loop impedances are quite often lower than the rest of the UK due to the larger numbers of substations, most MCB's in a domestic scenario are rated at 6 thousand amps withstand, however, there are some 10,000 amp ones available. Although a breaker may be rated at say, 32A, in the time it takes to trip, you can get massive currents flowing, potentially in the order of a few thousand amps, enough to do major damage! one important thing to remember, never open a switch or breaker on a fault, if you are ever unfortunate enough to close one and then realise there's a problem, DO NOT try and open it, let the fuse/breaker clear the fault,there are more injuries caused by attempting to open a circuit under fault than there are closing one. We were always taught the "left hand rule", if the handle on the unit was on the right, then operate it with the left hand, that way your body is to the right, and not in front of the unit, very handy if anything happens to go wrong, especially if the circuit is a few hundred amps.