Type A R.C.D. 6mA tolerant.

AJJewsbury: 
 

Are we to understand that the small D.C. current needed to drive a typical L.E.D. with series resistor, say 10-15mA, is enough to disable an A type R.C.D?

But it is reasonably difficult to inject such a d.c. current into a LV a.c. circuit - you'd need to create a complete loop/circuit for the d.c. current that included the a.c. circuit (or at least some path through the RCD) - so a single fault from something with a separated source (like a LED driver?) is unlikely to do it. A d.c. fault to earth with a simultaneous N-PE fault elsewhere is sort of the minimum I could imagine at the moment - but then we're into two-faults-to-danger territory, which is generally acceptable anyway (like an earth fault + a broken c.p.c.).

A few situations are riskier though - e.g. EV chargers where there's d.c. control/signalling circuitry that's deliberately referenced to the c.p.c. or where there are large d.c. currents wandering around exposed- and extraneous-conductive-parts  (e.g. returning traction currents on the Southern Railway) where a single fault could possibly create a d.c. circuit around a.c. conductors - i.e. the sort of situation where type B RCDs get specified (or some alternative like a RDC-DD in conjunction with an A-type RCD).

    - Andy.

Previous question repeated.

So, what level of D.C. current was injected by D-Lock earth fault impedance testers of old?

Quote. "To help explain, it might be worth thinking about some older models of earth fault loop impedance testers, which could cause the RCD to operate unintentionally. To prevent this, some types of earth fault loop impedance testers imposed a DC current on the AC test current. This DC current saturated the magnetic core of the RCD preventing it from tripping under the test condition.

Where equipment produces an element of residual DC, for example, variable-speed drives is connected to the electrical installation, the DC component can saturate the magnetic core and effectively blind or locks the RCD. This is known as ‘blinding’ and could either prevent the RCD from operating or reduce the sensitivity resulting in a dangerous situation."

Or did these testers inject ripply D.C?

Z.

AJJewsbury: 
 

Are we to understand that the small D.C. current needed to drive a typical L.E.D. with series resistor, say 10-15mA, is enough to disable an A type R.C.D?

But it is reasonably difficult to inject such a d.c. current into a LV a.c. circuit - you'd need to create a complete loop/circuit for the d.c. current that included the a.c. circuit (or at least some path through the RCD) - so a single fault from something with a separated source (like a LED driver?) is unlikely to do it. A d.c. fault to earth with a simultaneous N-PE fault elsewhere is sort of the minimum I could imagine at the moment - but then we're into two-faults-to-danger territory, which is generally acceptable anyway (like an earth fault + a broken c.p.c.).

A few situations are riskier though - e.g. EV chargers where there's d.c. control/signalling circuitry that's deliberately referenced to the c.p.c. or where there are large d.c. currents wandering around exposed- and extraneous-conductive-parts  (e.g. returning traction currents on the Southern Railway) where a single fault could possibly create a d.c. circuit around a.c. conductors - i.e. the sort of situation where type B RCDs get specified (or some alternative like a RDC-DD in conjunction with an A-type RCD).

    - Andy.

Previous question repeated.

So, what level of D.C. current was injected by D-Lock earth fault impedance testers of old?

Quote. "To help explain, it might be worth thinking about some older models of earth fault loop impedance testers, which could cause the RCD to operate unintentionally. To prevent this, some types of earth fault loop impedance testers imposed a DC current on the AC test current. This DC current saturated the magnetic core of the RCD preventing it from tripping under the test condition.

Where equipment produces an element of residual DC, for example, variable-speed drives is connected to the electrical installation, the DC component can saturate the magnetic core and effectively blind or locks the RCD. This is known as ‘blinding’ and could either prevent the RCD from operating or reduce the sensitivity resulting in a dangerous situation."

Or did these testers inject ripply D.C?

Z.