Upstream protection for short circuit current

jbrameld said:

This of course is not a simple matter as the product is CE/UKCA marked and such a modification would likely require a re-certification by the manufacturer with significant cost and time impacts.

Why do you need a CE marking? My understanding is that a CE marking is required to be applied by the manufacturer when selling a product within the EU/UK. I'm not aware of any requirement for the user to install only CE marked products - although I'm happy to be corrected.

Yes, the Noark datasheet doesn't provide any I2t data so not much to go off. One option could be to loop 10 (or so) meters of 25mm cable from the 80A protective device around the room and tell your consultant to recalculate the new PSCC at the terminals of the dimmer. 

only if they, (the manufacturer) think (well declare) that that specific standard applies.  Generally CE marking law does not form a complete set, even if folk are trying to follow it at all.
Mike.

Tim Boler said:

I was wondering the same. In the product data sheet of the dimmer panel link it doesn't make any mention of a maximum short-circuit current. The standards listed are:

EN61439-1, EN55015, EN61000-6-1, EN61000-6-2, ESTA DMX512-A/RDM.

Doesn't the manufacturer have to give the Icw or Icc per 61439?

Yes, Clause 6.2.1 of EN 61439-1 requires defined parameters of Clause 5 of the standard, including I_cw and I_cc, to be provided in technical information provided with the assembly ... for conditional short-circuit current, information on selection of an appropriate short-circuit protective device is also required.

I_CC is given in the Installation Manual as 6kA - unsurprising given the breaking capacity of the MCB's they use.  I have asked them for an energy withstand figure as the current figure on it's own is not the full picture.  That might give us a clue as to if the upstream protection may be adequate, or if we added tome BS88 fuses upstream that may sufficiently limit the energy let-through to a value that the dimmer way withstand.

jbrameld said:

I_CC is given in the Installation Manual as 6kA - unsurprising given the breaking capacity of the MCB's they use.  I have asked them for an energy withstand figure as the current figure on it's own is not the full picture.  That might give us a clue as to if the upstream protection may be adequate, or if we added tome BS88 fuses upstream that may sufficiently limit the energy let-through to a value that the dimmer way withstand.

I wasn't sure that makes 100 % sense ... and it doesn't, because I_cc is not quoted.

Instead, I_cw is quoted, along with I_pk, both at 6 kA, which, unless the manufacturer provides further information (a value for I_cc and a related OCPD specification) means there's no 'conditional rating' actually quoted in the manual, against which an upstream OCPD could be specified.

Explanation ... I_cc (where specified) is a conditional short-circuit rating, usually higher than I_cw and to achieve that rating an upstream short-circuit protective device, as specified by the manufacturer, is required for installations in which the prospective short-circuit current exceeds I_cw.

Sorry - my error in the subscript there.

Thanks for the explanation - very helpful as this is deeper into this subject than I have gone before.

If I interpret your post correctly, the manufacturer can provide an I_CC along with a condition (or set of conditions) that must be met for that rating to apply - e.g. an upstream OCPD specification.  Might that include for example a maximum energy let-through figure for the upstream device?

I'll follow that up with the manufacturer (along with the request for the 'internal resistance' value or the dimmer) and see where I get to.

Any other innovative solutions to this problem welcomed!

jbrameld said:

If I interpret your post correctly, the manufacturer can provide an I_CC along with a condition (or set of conditions) that must be met for that rating to apply - e.g. an upstream OCPD specification.  Might that include for example a maximum energy let-through figure for the upstream device?

Yes, or say a particular specification (standard, rating and type) of fuse etc.

jbrameld said:

(along with the request for the 'internal resistance' value or the dimmer)

I did have a thought about this ... and decided it's probably not worth pursuing, because if the fault occurs inside the dimmer, only part of, or perhaps little or none of, the internal resistance might be included in the short-circuit path, but we still would want to be happy the dimmer didn't set on fire or cause other hazards.

I can see where the suggestion came from, but with short-circuit current calculations in BS 7671 ('adiabatic') we consider a fault anywhere on the circuit. More traditionally, when a single fuse is used for a circuit, the "worst case" would be at the far end of the circuit (or a check at each end might do the trick) ... but with circuit breakers, or "combined protection" (two protective devices), things get more tricky, and the worst-case might be at the supply end of the circuit.

Yes - the internal resistance concept was originally based around the expressed concern that the MCB's, which are normally at the output, are only rated at 6kA and the PFC may be 9kA.  For that specific issue, the internal resistance would be in play, but your point about the assessment 'through the product' definitely widens the scope of that discussion. 

At the input to the dimmer, the wiring is protected by a 10kA rated device and I'm assuming the consultant has done his adiabatic correctly for that bit of the circuit, but the 'internal analysis' through the dimmer could be much more complex and would rely on the manufacturer.

If we don't get to an engineered and accepted solution the alternatives are not great for the project.  There is a 'bigger brother' ETC product with a much larger form factor that likely won't fit in the room and will have significant cost impact for the project.

yes, but in self certification route,  the design authority have to decide first which standards and secondly which bits of which standards are actually applicable to their case. Almost no-one uses the notified body route, so no-one external is marking the homework before going to market as it were, and the correct answer is not 'test everything' that is impossible to pass with conflicting requirements.

Being responsible for getting a product through CE marking can actually become incredibly stressful, as there is a serious risk of missing stuff that others may later decide is relevant or of failing something due to a test that actually should not have been considered relevant. It is  something I have occasionally had to do, and I don't like it.

There are a lot of occasions when you see  stuff that seems to be sold  with a CE mark  certificate and a rather 'oh sod it' short list of tests that may be deliberate, or just a limitation of the folk doing it.

Mike

"because if the fault occurs inside the dimmer, only part of, or perhaps little or none of, the internal resistance might be included in the short-circuit path, but we still would want to be happy the dimmer didn't set on fire or cause other hazards."

Yes, bur given its a steel box, one can very quickly set a very high bar, to the total liberated energy permissible, as all that is required is to contain the arc so the flash does not set fire to the curtains, and to catch all the flying bits  - nothing has to survive to work again, as by then it is a repair job anyway.

It may be informative to consider that more in the manner of a blast calculation.

Thinks like cheaper laptop power supplies use PCB track as open fuses for example, because the containment means it is fine.

Mike.

"because if the fault occurs inside the dimmer, only part of, or perhaps little or none of, the internal resistance might be included in the short-circuit path, but we still would want to be happy the dimmer didn't set on fire or cause other hazards."

Yes, bur given its a steel box, one can very quickly set a very high bar, to the total liberated energy permissible, as all that is required is to contain the arc so the flash does not set fire to the curtains, and to catch all the flying bits  - nothing has to survive to work again, as by then it is a repair job anyway.

It may be informative to consider that more in the manner of a blast calculation.

Thinks like cheaper laptop power supplies use PCB track as open fuses for example, because the containment means it is fine.

Mike.

mapj1 said:

Yes, bur given its a steel box, one can very quickly set a very high bar, to the total liberated energy permissible, as all that is required is to contain the arc so the flash does not set fire to the curtains, and to catch all the flying bits  - nothing has to survive to work again, as by then it is a repair job anyway.

It may be informative to consider that more in the manner of a blast calculation.

That is up to the manufacturer to consider that, it's outside the scope of BS 7671.

This is the rub for the installer.