I wasn't successful in tracking down the surge withstand strength information on the internet. It would be ironic if the introduction of AFDDs required the addition of SPDs!
See [Table 443.2]. Equipment which goes in a 230/400V DB needs to be able to withstand 4kV transients. (Meters, including smart meters, have to withstand 6kV!) One assumes manufacturers design their AFDDs to match.
I wasn't successful in tracking down the surge withstand strength information on the internet. It would be ironic if the introduction of AFDDs required the addition of SPDs!
See [Table 443.2]. Equipment which goes in a 230/400V DB needs to be able to withstand 4kV transients. (Meters, including smart meters, have to withstand 6kV!) One assumes manufacturers design their AFDDs to match.
I'm not sure that it's safe to assume anything associated with AFDDs!
This would be a great opportunity for the manufacturers to post their data sheets WITH the impulse withstand voltage.
I did find a data sheet for a combined MCB, RCD, AFDD with a 4kV impulse withstand quoted (co is called Eti and the device is an KZS-AFDD). I couldn't find the price!
I have just tidied up an existing installation for a long standing customer with over twenty rental properties, on this occasion it is for his own home.
Well the SPD part on its own seems to retail at about half that.
Inside the wylex and crabtree units are pretty much both like this teardown video by efixx .
I found the spring - loaded solder joint to disconnect and operate the warning flag and micro switch something of a throwback to a bygone era, that reminded me of the old tellys I used to sometimes repair as a teenager and in my early 20s.
In the screenshot below you can see how the L-E is a just a varistor (semiconductor transorb), the blue thing, and NE is the gas filled ceramic cylinder with metal caps at both ends - a sort of enclosed 'spark gap' of more controlled behaviour if you will.
regards Mike
edit PS
For those few of us who like to design the same level of protection into our own equipment and enclosures one can get similar transorb varistor parts offering the same functionality, including the warning microswitch output built in like these with solder tags for about 15 -20 quid in modest quantities (falling to about half that in bulk).
Quite a bit less if you do not want the warning output.
Non rupturing up to 200kA apparently. Part of me would like to see that spec tested, but as it is a limit many substation fuses might not meet anyway, this is not one to trouble the scorers.
The high current gas discharge tubes are quite a bit cheaper ( examples ), at 1/3 to 1/2 the price of the varistor parts depending on model chosen.
I tried pricing the components to assemble on site, the SPD is available at a reasonable price, but when everything is collected together the price isn't silly.
Maybe the days of consumer units being available for less than a hundred quid are numbered and Joe Public is about to get a wake up call?
Why should a CU be cheap? In the context of a whole building, the wiring is really quite good value. For example, how does the price of a basic CU compare with a window? Yes, just one window.
I have been fitting CPFUSEBOX consumer units (around £80) with Type A RCBOs (around £12 ea+VAT) and built-in surge - not too expensive. Since I have no intention to pander to the manufacturers bottom lines I will not be in the mkt for anything AFDD related in future, since the Deviations column on the cert is ample enough.
