Following a few debates here, and in other places about whether over-current protection is required for SPDs, BEAMA issued a statement in January saying, extra OCPDs are not always required for SPDs. Full details in the link below.
As an aside, I do check the BEAMA site semi-regularly, but didnt spot this one until I had an email from Dehn yesterday.
I wonder what the suppliers'/DNOs' position is on this. How often do SPDs go short circuit?
Thanks Alan for posting this. I also first heard about it in the Dehn circular yesterday. One to slip between the pages of the brand new orange book which arrived yesterday?!
I wonder what the suppliers'/DNOs' position is on this.
If the ENA are involved then assumedly the individual DNOs are okay with it?! Or at least a majority are.
What happens when the SPD type 2 expires and needs replacement, possible exposed parts when the cartridge is removed?
What happens when the SPD type 2 expires and needs replacement, and the cartridge CAN NOT be removed due the effect of thermal damage?
What happens when people don't know the difference between an
SPD Type 1?
SPD Type 2?
SPD Type 3?
The ENA/BEAMA statement has a number of conditions on which the permision is contingent, one of which being that the "SPD does not require withrawal of the DNO cut-out for its replacement or maintenance". How that is achieved (provision of a means of isolation, one assumes, if the cartridge exposes live parts) is left to the installer.
As for not knowing the difference between type 1/2/3... that risk isn't changed by allowing the DNO cut-out fuse to be the OCPD.
What happens when the SPD type 2 expires and needs replacement, possible exposed parts when the cartridge is removed?
As the guidance said - "The SPD does not require withdrawal of the DNO cut-out fuse for its replacement or maintenance." All the plug-in SPDs I've seen mate with bases that provide at least finger-proof protection to live parts.
What happens when the SPD type 2 expires and needs replacement, and the cartridge CAN NOT be removed due the effect of thermal damage?
I guess the same as happens when there's thermal damage to any part upstream of outgoing devices - switch off if you can (just because there's no OPD doesn't mean you can't use the main switch or supplier's isolator) - failing that call out the DNO.
What happens when people don't know the difference between an
SPD Type 1?
SPD Type 2?
SPD Type 3?
They shouldn't be messing with things they don't understand?? Most SPD cartridges are keyed so the wrong types can't be inserted into a correctly installed base - mostly to stop L-N types (MOV) being used in N-PE situations (gas discharge), but I suspect will stop most such mistakes.
- Andy.
To be honest I think there SHOULD be a OCPD for a Type 2 SPD in the CU (Consumer Unit) and not relying on the DNO/DSO cut out main fuse due to the following
It provides OCPD protect to the SPD
It provide a means of safe isolation/Authoritative control for replacement or servicing as required in many place by BS7671
eg. Isolation and Switching (Part 5): Every installation must have a main switch to cut all live conductors
eg. Maintenance Isolation: Devices must be provided to allow safe disconnection of electrical equipment for maintenance, such as local isolators for motors or appliances
Thus an OCPD is reasonably practicable and sound engineering judgement. If not this will turn into another whole debacle of single insulated cables in a meter box/cabinet being allowed and no EICR code. Remember we need to use our engineering judgement
To be honest I think there SHOULD be a OCPD for a Type 2 SPD in the CU (Consumer Unit) and not relying on the DNO/DSO cut out main fuse due to the following
At least they have not been banned, so mine is staying where it is.
It provides OCPD protect to the SPD
I don't think that's the intention at all - suitable SPDs have in-built overcurrent protection. Not only that the in-bult protection is specifically designed not to trip during short high current events - just the sort of thing MCBs are good at tripping on and what SPDs should protect from but won't if the MCB has opened when it didn't need to.
Isolation - the main switch is still there, before the SPD - so little advantage there (on TT if you need to isolate you'd need 2 pole device anyway, so a simple SP MCB wouldn't benefit).
- Andy.
It provides OCPD protect to the SPD
I don't think that's the intention at all
So what is/was the intention?
I must say that these things are like air-bags: you will probably never use one.
Isolation - the main switch is still there, before the SPD - so little advantage there
What about BS 7671 Regulation 314.1 inconvenience?
my personal engineering judgement goes along the lines of - if there is a switch or MCB in series with the surge arrester, when is it turned off ? When the SPD has failed short circuit, and its internal fuse wire or similar trip has not operated, or by mistake when the householder turns off the wrong thing, and does not notice.
I can see an argument for no dedicated breaker, rather like the argument for not putting fire/ smoke alarms on an MCB that may be turned off and stay off, but better with say the lights, as those might actually be noticed if not working.
The blowing of the company fuse will in all but the silliest of situations be a red herring - the SPD element will fail short, but something in series with it will then open promptly, and so long as the designers have made the enclosure to contain the bits that's all fine. The company fuse will also go for shorts to the live bus bar or stuck MCBs, but that is equally very rare and we dont worry about it.
I'd expect the din mounted SPD holder to have a similar life span to a cheap MCB or RCD, .and changing it to be a similar board-open operation, while the SPD itself is intended to be unplugged as an unskilled like for like replacement. Hardest part seems to be getting a replacement module without the din rail mount.
Seems reasonable enough to me.
Mike
my personal engineering judgement goes along the lines of - if there is a switch or MCB in series with the surge arrester, when is it turned off ? When the SPD has failed short circuit, and its internal fuse wire or similar trip has not operated, or by mistake when the householder turns off the wrong thing, and does not notice.
I can see an argument for no dedicated breaker, rather like the argument for not putting fire/ smoke alarms on an MCB that may be turned off and stay off, but better with say the lights, as those might actually be noticed if not working.
The blowing of the company fuse will in all but the silliest of situations be a red herring - the SPD element will fail short, but something in series with it will then open promptly, and so long as the designers have made the enclosure to contain the bits that's all fine. The company fuse will also go for shorts to the live bus bar or stuck MCBs, but that is equally very rare and we dont worry about it.
I'd expect the din mounted SPD holder to have a similar life span to a cheap MCB or RCD, .and changing it to be a similar board-open operation, while the SPD itself is intended to be unplugged as an unskilled like for like replacement. Hardest part seems to be getting a replacement module without the din rail mount.
Seems reasonable enough to me.
Mike
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