Energy let-through for Type 2 MCB's ?

It is a fairly safe assumption as that series including the LN5932 morphed into the more modern B and C breakers with little change except some new screen printing.

This article on what to assume about old breakers  may be vaguely interesting . The basic gist is that old breakers are OK, if you  know the characteristics.

Mike.

The 15th edition has time current charts for B.S. 3871 type 2. The breakers there, are though, 30 Amp rated.

www.ebay.co.uk/.../648837690

Edit. Add. The 16th edition has the curve for the 32 Amp breakers to B.S. 3871. It runs very close to the 30 Amp M.C.B. curve. Fig. 3.5.

Time current characteristics for B.S. 3871. 

0.1 to 5 seconds. 224 Amps. For a 32 Amp. M.C.B. Type 2.

Z.

And..........as I have found a M.K. LN5910 here I have read the details printed on it.  MADE IN ENGLAND. LICENSE SIEMENS.

M3. Ref. calibrated temp 20 degrees C.

Z.

The 16th edition has the curve for the 32 Amp breakers to B.S. 3871. It runs very close to the 30 Amp M.C.B. curve. Fig. 3.5.

Time current characteristics for B.S. 3871. 

0.1 to 5 seconds. 224 Amps. For a 32 Amp. M.C.B. Type 2.

Unfortunately what you need for energy let-though is the "instantaneous" response - which is mostly off the scale of those graphs - which flat-line at either 0.01s or 0.02s depending on which edition (which seems dubious in itself). If you did try to apply those graphs directly the energy let-though would be simply proportional to the square of the fault current without limitation - so you'd often get implausibly high values - e.g. 3kA fault current for 0.02s gives 180,000A²s - compared with say 18,000A²s for a 32A B-type according to BS EN 60898.

    - Andy.

Indeed. I find that if I apply a 30K A^2s (which would be the approximate case for 32A type C in this location), then I'd be just OK. On that basis I'm assuming that the type 2 32A (Yes it is 32A not 30A) will be fine. 

Regards

Anything above 3kA fault current will probably blow the breakers up. They are M3 rated.

And prey tell please, why do we need the energy let through info. on these domestic sized M.C.B.s?

Z.

Anything above 3kA fault current will probably blow the breakers up. They are M3 rated.

OK do the calculation for a 2kA or 1.5kA  fault current then if you prefer - it's still likely to be more than would reasonably be expected.

Besides these MCBs are presumably in a CU that has an overall rating of 16kA, so it's probably not a safe assumption that all fault currents will be below 3kA.

And prey tell please, why do we need the energy let through info. on these domestic sized M.C.B.s?

Presumably to confirm that reduced c.s.a. conductors meet the requirements of the adiabatic?

   - Andy.

AJJewsbury said:

And prey tell please, why do we need the energy let through info. on these domestic sized M.C.B.s?

Presumably to confirm that reduced c.s.a. conductors meet the requirements of the adiabatic?

I think that the point that Zoomup is making is how often in a domestic installation would you be selecting the conductor size of the CPC? How often would you be wiring in singles?

I think that the point that Zoomup is making is how often in a domestic installation would you be selecting the conductor size of the CPC? How often would you be wiring in singles?

The adiabatic isn't just for singles - most T&E cables have reduced c.p.c.s - 1.5mm² (or even 1.0mm² if it's an older 2.5mm²) on a 32A device isn't an automatic pass if the fault currents could be high.

   - Andy.

As Andy says. And there are a lot of old installations about, often needing judgements, especially for EICR and minor upgrades to poorly structured installations.