Non-selective RCD with SPD downstream

[pabrinex]

Hi all,

Grateful for your expertise regarding my confusion on the below.

Context:

• French rural domestic property
• Single phase supply, TT earthing
• Supplier side RCBO (standard in France, usually next to the meter) - "disjoncteur de branchement" - 500mA, single pole protection, unspecified type
• This supply-side RCBO is actually inside the property, whilst the meter is in the box outside (other side of wall)
• The current install is probably original and from the 1990s

Plan to fit a new consumer unit with all circuits protected by 30mA type A or type AC RCDs
Would like to fit a surge protection device Type 2 (it is on the border of one of the departments where a "parafoudre" is mandatory for lightning protection)

Most of the French guidance on installation of SPDs suggests fitting at the bottom of the consumer unit, directly downstream of the main RCBO (and therefore in parallel with the rest of the RCD protected final circuits). It seems that it is now standard for supply-side RCBOs are Type S, but this one is not.


"Regulation 534.4.7 states that an SPD installed on the load side of the RCD is required to have a surge current immunity of at least 3 kA.

RCD standards include two levels of immunity to surge currents.
1. A General type RCD with a minimum surge current immunity of 200 A with a 0.5 µs/100 kHz waveform (Various Types)
2. A time delayed S type RCD with a minimum surge current immunity of 3000 A with an 8/20 µs waveform
Therefore, an SPD should not be installed on the load side of a G type RCD, this is to prevent unwanted operation of the RCD due to surge current."

Aside from the beneficial selectivity (discrimination) of having a Type S with the in-series RCDs of the final circuits, what is the relevance/importance of Type S in use with SPD? Presumably if the supply-side RCBO is not surge current immune as above, then it would trip during a surge and somewhat inhibit the ability of the SPD to pass to earth (though I imagine with a surge large enough it would arc across the switch).

Finally, the current supply-side RCBO has the symbol discussed here:

Anyone know this RCD symbol?

Hi guys, I know the AC symbol but the one to the right i've not seen before or just not noticed it. Anyone know?

www.electriciansforums.net

The final comment suggests that a general type RCD with the symbol would: "... will resist surges 8/20μs up to 250A"
Can anyone shed any more light on this symbol, and whether perhaps the current supply-side RCBO is in fact immune to surge currents mentioned above?

I will be applying to ERDF for the supply-side RCBO to be upgraded to a Type S for selectivity, but in the interim, I'd be grateful for your thoughts on the relevance of a non-selective RCD upstream of an SPD.

Many thanks!

 

[pc1966]

I think you can be fairly certain that the supply-side RCBO is a selective type. There are two reasons I think for the SPD not being downstream of a 30mA RCD, one is the likelihood of it tripping on a surge, the other is traditionally type-S with high current types intended as main switch, so I presume less chance of contacts welding due to the surge current.

Which is bad news for safety!

I would say if you are in rural France then you should look carefully at the lightning risk and probably go for a type 1+2 SPD in spite of the greater cost as it will last far longer and actually do its job without having to be constantly monitored and SPD modules replaced if burned out. Not only is France more prone to lightning than UK, but rural settings typically have overhead supply lines and those pick up more energy from indirect strikes.

Direct strikes are very bad news all round, but far less likely unless you are a tall isolated building, etc, in which case you should have a Lightning Protection System (LPS). If you want to read more about this then this catalogue has a lot of good information (large 17MB PDF download):

https://www.nvent.com/sites/default/files/acquiadam/assets/E907W-WWEN.pdf

You might find you can't fit a type 1+2 SPD within your CU, in which case it can go in a DIN box with a main switch, etc, as an alternative. Many of that type have double terminal (known as Kelvin or V-wiring) and the best use it to route the supply to one and load to the other, it cuts down on cable length and hence inductance, improving protection. We have used 3-phase SPD from these folks, in your case something like this might be a good choice to cope with lots of energy:

Type 1+2 Lightning Current and Surge Arrester (KM1+2-25-1+1 SC) - Kingsmill Industries

System: Single Phase TT/2 Pole Nominal Voltage: 230V AC

kingsmillindustries.com

This is its smaller brother: cheaper, also type 1+2, but of course less capacity for big surges:

Type 1+2 Lightning Current and Surge Arrester (KM1+2-12.5-1+1 SC) - Kingsmill Industries

System: 1 Phase TT/2 Pole Nominal Voltage: 230V AC

kingsmillindustries.com

A good short/direct route to the earth rod is also important, so placing this close to the incoming supply position and running the cable direct to a rod outside is probably your best option.

After the SPD then your usual CU arrangement for France should be fine, with double-pole RCBO, etc.

 

[pabrinex]

I think you can be fairly certain that the supply-side RCBO is a selective type. There are two reasons I think for the SPD not being downstream of a 30mA RCD, one is the likelihood of it tripping on a surge, the other is traditionally type-S with high current types intended as main switch, so I presume less chance of contacts welding due to the surge current.

Which is bad news for safety!

I would say if you are in rural France then you should look carefully at the lightning risk and probably go for a type 1+2 SPD in spite of the greater cost as it will last far longer and actually do its job without having to be constantly monitored and SPD modules replaced if burned out. Not only is France more prone to lightning than UK, but rural settings typically have overhead supply lines and those pick up more energy from indirect strikes.

Direct strikes are very bad news all round, but far less likely unless you are a tall isolated building, etc, in which case you should have a Lightning Protection System (LPS). If you want to read more about this then this catalogue has a lot of good information (large 17MB PDF download):

https://www.nvent.com/sites/default/files/acquiadam/assets/E907W-WWEN.pdf

You might find you can't fit a type 1+2 SPD within your CU, in which case it can go in a DIN box with a main switch, etc, as an alternative. Many of that type have double terminal (known as Kelvin or V-wiring) and the best use it to route the supply to one and load to the other, it cuts down on cable length and hence inductance, improving protection. We have used 3-phase SPD from these folks, in your case something like this might be a good choice to cope with lots of energy:

Type 1+2 Lightning Current and Surge Arrester (KM1+2-25-1+1 SC) - Kingsmill Industries

System: Single Phase TT/2 Pole Nominal Voltage: 230V AC

kingsmillindustries.com

This is its smaller brother: cheaper, also type 1+2, but of course less capacity for big surges:

Type 1+2 Lightning Current and Surge Arrester (KM1+2-12.5-1+1 SC) - Kingsmill Industries

System: 1 Phase TT/2 Pole Nominal Voltage: 230V AC

kingsmillindustries.com

A good short/direct route to the earth rod is also important, so placing this close to the incoming supply position and running the cable direct to a rod outside is probably your best option.

After the SPD then your usual CU arrangement for France should be fine, with double-pole RCBO, etc.

Hi pc1966,

Many thanks for your detailed reply.

I will definitely take your advice on considering a better SPD.

I attach a photo of the current supply-side RCBO just in case you can identify it any better. My googling hasn't yielded any specific details, but it doesn't carry the S symbol of selectivity, so I'm not convinced.

With regards to the earthing, the earth rod is actually very close to the supply-side RCBO, but not the consumer unit (approx 10m away). Where relocating the CU isn't feasible, I presume therefore it is better practice to mount the SPD separately in an enclosure as you mentioned, near the earth rod, in parallel to the supply to the CU, with it's own protective conductor to the MET equivalent at the rod?

Many thanks

 

[happysteve]

Just a thought, could you not test the incoming RCD with a tester to determine its trip times, and hence whether it's selective or not?

 

[pc1966]

I will definitely take your advice on considering a better SPD.

Many also have aux contacts that can be used to generate a warning (indicator light or some fancy building management system to email/text you) if failed, but it might be cheaper just to go for a high rated one from the start!

I attach a photo of the current supply-side RCBO just in case you can identify it any better. My googling hasn't yielded any specific details, but it doesn't carry the S symbol of selectivity, so I'm not convinced.

I has the funny 'shark fin' symbol though. Others of similar spec do say selective:

https://www.manomano.fr/p/disjoncteur-edf-2p-15-45a-diff-500ma-selectif-1705777

Disj.branch. diff. 2P 15/45A 500mA sel. • HDE245S | Hager

Trouvez des produits Hager, Disjoncteur de branchement différentiel 2P 15/45A 500mA selectif et plus chez Hager France

hager.com

With regards to the earthing, the earth rod is actually very close to the supply-side RCBO, but not the consumer unit (approx 10m away). Where relocating the CU isn't feasible, I presume therefore it is better practice to mount the SPD separately in an enclosure as you mentioned, near the earth rod, in parallel to the supply to the CU, with it's own protective conductor to the MET equivalent at the rod?

That is what I would do.

If you have a very big installation with sub-DB located tens of meters away, etc, there is a case for those having internal type 2 SPD, but for typical home having protection at the incoming point is sufficient.

I would also add copper phone lines, etc, are also potential sources of inducted current that can cause trouble as well. Obviously if you have fibre broadband that is not an issue, but I doubt it in many rural areas! I don't know how France deals with it, the UK used to put GDT in the first "main socket" phone point for protection but recently that seems to have been dropped. You can buy devices, but as for most surge protection you want them at the building entry point with short route to true Earth.

If exposed then TX/satellite antennas high up are potential lightning rods so they ought to have some direct high current path to earth like copper or aluminium tape etc. At least the coax cable should be earthed before it enters the building (e.g. using a bulkhead adaptor(s) on earthed metal plate, ideally with surge protective devices as the adaptors, but even just F-F with M plugs on cable either end will do for earthing).

 

[pc1966]

On phone protection:

Phone line SPD on budget

Following the tragic tale from @telectrix about lightning damage to phones and modem leading to a serious loss of beer money I decided to take a look at an el-Chepo SPD from Amazon to see if it looks worth considering. This one: https://www.amazon.co.uk/dp/B08FRN2569 When it arrived the box...

www.electriciansforums.net

 

[pc1966]

I attach a photo of the current supply-side RCBO just in case you can identify it any better. My googling hasn't yielded any specific details, but it doesn't carry the S symbol of selectivity, so I'm not convinced.

The other way to look at this problem is - it is not your problem.

The "disjoncteur de branchement" is supplied and owned by the electricity company and so it has to cope with any SPD or similar in your installation. If it trips on a large surge then you simply have to reset it. If it breaks due to the surge that is the supply company's problem.

TL;DR you cant change it so have to live with it.

 

[pc1966]

If spending significant money on TV / satellite / cable modem protection this is the sort of surge protector that is ideal, as bulkhead mounting and able to be sealed:

https://www.polyphaser.com/type-f-surge-protector-2.5ghz-2ghz-gas-discharge-tube-gt75-fff

However, price tag and USA supply might be issues.

If buying from Amazon (as more or less last resort usually!) then this is an option:

https://www.amazon.co.uk/Lightning-Arrestor-Cellular-Satellite-Arrester/dp/B0772TXBCQ/ref=sr_1_2

The female-female type is easier to use as you simply put a couple of F-type plugs on the cable at the point it is inserted. However, it is not waterproof, and the use of the red crimp (1.5mm max) is hardly adequate. I would use at least 4mm on yellow crimp in its place. Again, it ought to be outdoors (before coax enters property) and located so short/direct route to Earth, so some sort of a box that keeps the water off (and cables dipping down then up in to box to stop water running that way) is needed.

Another tip is to use some Vasiline or silicone grease on the coax connectors thread before doing them up, and (after wiping down connector and your hands) some self-amalgamating tape over the cable, connector, and exposed thread afterwards to keep as much water out as practical.

 

[pabrinex]

Just a thought, could you not test the incoming RCD with a tester to determine its trip times, and hence whether it's selective or not?

Just a very sensible thought! I'm visiting the property this week coming so will let you know the outcome.

 

[pabrinex]

The other way to look at this problem is - it is not your problem.

The "disjoncteur de branchement" is supplied and owned by the electricity company and so it has to cope with any SPD or similar in your installation. If it trips on a large surge then you simply have to reset it. If it breaks due to the surge that is the supply company's problem.

TL;DR you cant change it so have to live with it.

I'm very grateful for all of your detailed messages, thank you.

As mentioned above, I will test the RCD and determine its selectivity and then if not, request for it to be changed (not sure how likely Enedis, previously ERDF, is to do this in the absence of any fault).

As far as fibre goes, its actually fairly good in France.. though at this property I believe it's fibre-to-the-telegraph pole. Where this fibre-copper transition is say, < 50metres to the property, do you think that would reduce the risk sufficiently to not need phone-line SPD?

 

[Mike Johnson]

Sorry downloaded the wrong wiring diagram will look for the correct one approved by Endis, but would add we always unplugged the phone when a storm was brewing or we left for extended periods.

 

[pc1966]

As far as fibre goes, its actually fairly good in France.. though at this property I believe it's fibre-to-the-telegraph pole. Where this fibre-copper transition is say, < 50metres to the property, do you think that would reduce the risk sufficiently to not need phone-line SPD?

The issue is how is that powered? If it is fibre to the pole but also overhead power to same pole to do the fibre-copper media conversion you don't quite escape the induced surge issue.

But it might be far less if earthed locally.

Again, some local experiance/history might tell you how often modems get blasted and if it is on your cost to replace, etc.

 

[pabrinex]

For anyone interested, I tested the supply side RCBO today and got a 1x I time of <130ms, so I don't believe it is a Type S. I did however have some downstream higher sensitivity 30mA RCDs which did trip during testing the existing circuits, and the supplier RCBO was fine, so who knows.

pc1966 - I did as you suggested and mounted the SPD immediately after the RCBO and right next to the earth rod, in parallel with the CU which is 10m away, it seems to have worked nicely!

Finally, we had the fibre installed right into the property (FTTH) !

Thanks all for the help.