Wylex 3 phase board fitting.

[oscar21]

Do I need any more than this to fit the above board, does it need a fitting kit for the switch or anything extra to get it up and running (tails excluded obviously)

 

[westward10]

No.

 

[oscar21]

Thanks, will order it all then.

 

[Flanders]

Are you using every way if not you will need done blanking modules and check if you need surge protection

 

[oscar21]

Are you using every way if not you will need done blanking modules and check if you need surge protection

Got loads of Wylex metal blanks, I presume they will fit in. As for surge, I'm going to fit a 3rd party one in an external enclosure, the price of the wylex one is ridiculous. Thats if it needs a SPD at all, not too sure of the commercial regulations.

 

[pc1966]

Thats if it needs a SPD at all, not too sure of the commercial regulations.

It is, almost certainly it will fall under 443.4.1 section (iii) "significant financial or data loss" if something business-critical stops working as a result.

Having said that, for £160 or so I can't imagine you will save that much once you add up the cost of parts and your time to do a 3rd party DIN box compared to the internal kit:

Wylex NHTNSP125L 125A 10kA Integral Surge Arrester Kit

Buy Wylex NHTNSP125L 125A 10kA Integral Surge Arrester Kit from Falcon Electrical UK a leading electrical wholesaler

www.falconelectrical.co.uk

From TLC:

125A 10kA Integral Surge Arrester Kit | Wylex (NHTNSP125L)

 

[westward10]

Use the correct blanks those metal consumer unit blanks will just slide down when fitting or fall out when someone removes the cover which could be dangerous.

Solid Cover & Busbar Blank Plate 1G for 3 Phase | Wylex (NHBLM1L)

 

[ipf]

No.

Keep it basic, to suit the question.

 

[oscar21]

Use the correct blanks those metal consumer unit blanks will just slide down when fitting or fall out when someone removes the cover which could be dangerous.

Solid Cover & Busbar Blank Plate 1G for 3 Phase | Wylex (NHBLM1L)

The newerclip in Wylex blanks are a big improvement on the others, they grip the sides quite firmly now. As you say the older type used to slide about all over the place, it was hard enough even trying to get a horizontal cover on with them in never mind a vertical one. I will look into the proper blanks for that unit though.

 

[oscar21]

It is, almost certainly it will fall under 443.4.1 section (iii) "significant financial or data loss" if something business-critical stops working as a result.

Having said that, for £160 or so I can't imagine you will save that much once you add up the cost of parts and your time to do a 3rd party DIN box compared to the internal kit:

Wylex NHTNSP125L 125A 10kA Integral Surge Arrester Kit

Buy Wylex NHTNSP125L 125A 10kA Integral Surge Arrester Kit from Falcon Electrical UK a leading electrical wholesaler

www.falconelectrical.co.uk

From TLC:

125A 10kA Integral Surge Arrester Kit | Wylex (NHTNSP125L)

The problem with this job is its 2 buildings into one, I think I posted a thread on it a while ago. Its one building with one entrance door but it has two of everything including incoming supplies/meters. The customer wanted it wiring this way so there are two mains units, one for the left half and one for the right half. I take it it would need an SPD on both units, I'm not even sure where the 2nd supplies comes from, its not looped from the other supply and looks newer than the original one.

 

[pc1966]

The customer wanted it wiring this way so there are two mains units, one for the left half and one for the right half. I take it it would need an SPD on both units, I'm not even sure where the 2nd supplies comes from, its not looped from the other supply and looks newer than the original one.

Yes, you are looking at separate SPD for each half.

If you had a common incoming point, such as an isolator switch feeding Henley blocks that then split to the different DB, you could place a common SPD there.

In all cases you need to keep the SPD cable loop length to 0.5m max (so L => SPD => E and L => SPD => L or N) for the SPD to be effective (see 534.4.8) as what impacts on performance most of all is inductance since the surges have most power at relatively high frequency compared to 50Hz power (around 100kHz). That is why your neighbour's SPD will do little to protect you even if it is on the same phase.

The inductance is also why you don't want coiled up cables feeding the SPD, and ideally you want to use high current, and C or D curve, MCB to reduce the magnetic trip coil's impact as much as you can. Or no MCB at all if the SPD is safe for your incoming fuse and you have an approved method of connecting it (such as neutral blocks in place of MCB to a busbar, or like the Hager kit that links across the incomer's connections, etc).

 

[pc1966]

I will look into the proper blanks for that unit though.

What I like about the MCB-like blanks is they help you get the correct MCB spacing while screwing the busbar point if you have combinations that leave gaps (e.g. TP then (1-2)*SP then TP in a set of 3, etc).

You just need to check that one end is correctly lined up with the cover's hole to begin with, and later the cover ought to fit nicely and any future addition can be done without having to move any about.

 

[ipf]

What I like about the MCB-like blanks is they help you get the correct MCB spacing while screwing the busbar point if you have combinations that leave gaps (e.g. TP then (1-2)*SP then TP in a set of 3, etc).

You just need to check that one end is correctly lined up with the cover's hole to begin with, and later the cover ought to fit nicely and any future addition can be done without having to move any about.

Never used to be such major problems...Just no fuse wire or cartridge in the carrier....

 

[oscar21]

I remember watching a John ward video a while ago on SPD's and cable length and kind of understood it at the time but it just doesn't make sense to me now. The surge must originate outside the building somewhere and is brought in by the main cable I guess. This main cable could be any length from a few metres to a few kilometers and also the tails might be 500mm or 3 metres and yet the last bit of the wiring to the SPD cant exceed 500mm.

What does this achieve, to me its like putting your solar panels on the roof to be closer to the sun thats 93 million miles away.

 

[pc1966]

What does this achieve, to me its like putting your solar panels on the roof to be closer to the sun thats 93 million miles away.

You have to remember that the SPD is trying to divert the surge current. So if the supply goes above 500V-ish it starts to conduct rapidly and in order to dump a few kA of surge, and at for no more than a kV or so of let-through voltage, it has to have a dynamic impedance (dV/dI) of under an ohm.

But that all happens very quickly (tens of microseconds), so if the SPD's cable has any significant inductance that make the SPD look like a higher impedance, so you get less current diverted and so a bigger voltage let-through.

The SPD and its cable is a shunt across the supply, so the length of supply cable feeding it is not important, it is the length of cable between the supply L/N/E and the SPD terminals that determines how well it is able to shunt that current away (heating up internally in the process).

 

[suffolkspark]

Presumably the hager rcbo in your screenshot is for a different job?

Just get the wylex spd kit, so much tidier.

 

[oscar21]

Presumably the hager rcbo in your screenshot is for a different job?

Just get the wylex spd kit, so much tidier.

No, bollox, must have clicked the wrong link

 

[oscar21]

You have to remember that the SPD is trying to divert the surge current. So if the supply goes above 500V-ish it starts to conduct rapidly and in order to dump a few kA of surge, and at for no more than a kV or so of let-through voltage, it has to have a dynamic impedance (dV/dI) of under an ohm.

But that all happens very quickly (tens of microseconds), so if the SPD's cable has any significant inductance that make the SPD look like a higher impedance, so you get less current diverted and so a bigger voltage let-through.

The SPD and its cable is a shunt across the supply, so the length of supply cable feeding it is not important, it is the length of cable between the supply L/N/E and the SPD terminals that determines how well it is able to shunt that current away (heating up internally in the process).

That makes sense thanks, must have been what JW was getting at ut I couldn't remember it.

 

[pc1966]

Here is an attempt to make the SPD wiring effect more obvious:

The surge on the supply is usually limited on LV networks to around 6kV open-circuit as above that something upstream will tend to flash over. While the supply cable impedance tends to 50-80 ohms for long lengths (its characteristic impedance), for 100kHz that is longer than 2km so not likely, and for shorter cables (i.e. surge closer to the SPD) it looks close to some R & L and often is as low as an ohm or so, so the surge current is often taken as around the 3kA or so region.

So your typical surge might be of the order of 3kA and 1.5kV over the SPD which is about 4.5 MW. While that is a lot of power, it is typically only for around 20us or so, so represents about 90 J of energy/heat.

Looking up zinc oxide as the typical material for a MOV surge protective device, if we take it as weight about the same as a 20p coin = 8g then it is about 0.1 mole of compound. The heat capacity is given as 40.3 J/K/mol so such a 90J surge will heat the disk up by about 23 K which is easy to survive.

Doing the same for the ~350us surge from a direct hit on to some aspect of the power system (or local ground linked to a lightning conductor), instead of the ~20us from a nearby strike inducing current, you have a disk temperature of hitting about 410 C and so melting the contacts for safe disconnecting. Next hit and your electronics is toast...

The bigger type 1(+2) SPD often use GDT (gas discharge tube) so when they fire the volts drop down to ~100V to keep the device's dissipation down by a factor of 10-15 compared to a MOV that tries to tough it out, but they have issues of mains AC current follow-through so sometimes have a lower voltage MOV in series to try and let any arc quench on the AC zero-crossing much faster, etc.

But looking at the lower circuit you can see that the L of the SPD's cables is in series with the surge current, so the volt drop along their inductance is presented to the load. Which it might not enjoy.

 

[oscar21]

Thanks for the explanation, I'm not sure I understand everything but sort of get it, I've watched big clive tear down SPD devices before now and ween the gas discharge tubes inside them. I think the simplest explanation is it matters how short the cables are when they are across the mains as opposed to in-line with them.