Lightning, spds and rcds

[mhar]

Went to a property today where the lady is having problems with a 30mA rcd tripping during lightning. This is an upfront rcd protecting a small db in a large metal roofed garage which feeds 1)garage sockets, 2)garage lights, 3)electric gates and 4) fish pond equipment. It is the gates being disabled when the rcd trips that is the problem as she is in her 60's, recently widowed and past her gate jumping days.
I only had access to the garage where she left me installation certs mainly dated 2008 which showed a tt system with a Ze of 48 Ohms on one and 62 on another. On one of the certs it stated that this rcd had been removed but reinstated by the person doing the work. The house has had an extension 3-5 years ago and I assume the earthing was converted to pme as my Zrcd was .37Ohms, I was not left a cert covering this work. Obviously I have further investigations to do next week but it appears that the problem has been around for quite a few years and the earthing system is probably not relevant, the cpc had also been disconnected in the rcd enclosure. The rcd ramps at 21-24mA
I have been thinking along the lines of inserting an spd (Wilts controlgear SS40) between the rcd and the db to protect the rcd from what I assume to be large voltage spikes. My other options being replacing the t&e gate feed with swa so I could have an unprotected feed but this would allow spikes to pass to the house cu, or use four rcbo's and hope that the spikes are not originating from the gate circuit (which is a bit hit and miss for me).
I would be interested in how others have approached similar situations. App 18 of bgb shows spds on the load side of an rcd as I am thinking, I have never dealt with one before. My question is basically about the suitability of this spd, it's likely effectiveness and any other considerations there may be.
Have to go out shortly so there may be a delay in replying.

 

[telectrix]

my initial thoughts would be to feed the gates with SWA, fed from a non-RCD MCB as long as that part of the installation is not TT earthing.

 

[UKMeterman]

Is this RCD in the garage? If so split the load with rcbos, so the fish pump and others are separate from the gates. Is the metal work of the garage bonded to the supply?
Any IR issues?
Is the supply now PME or TN-S or TT?

 

[mhar]

Thank you. That was my option no 2. However my concern was that any voltage spikes would then have a path into the main cu. I suppose SWA terminated into an ip rcd at the gates would stop this and the rcd would be accessible to her from outside the gates. Am I overly concerned about these spikes?

 

[Octopus]

Remove up front RCD, MCB for gates, RCBO's for the other circuits.

 

[telectrix]

Remove up front RCD, MCB for gates, RCBO's for the other circuits.

agreed, but he'll need to replace the T/E to the gates with SWA unless it's run in earthed metal conduit.

 

[Octopus]

agreed, but he'll need to replace the T/E to the gates with SWA unless it's run in earthed metal conduit.

Why? if its surface run there is no need for RCD's

 

[mhar]

Thanks for the replies.
My concern is that if I do not have any type of rcd or spd (the current rcd is acting as a surge protector) then any spikes will travel to the main cu and trip any rcd there leaving us worse off than now. She will be stuck outside her gates whilst her freezer is defrosting!
I have never used an spd before, the one I referenced is £30 and looks like a solution that ticks all my boxes.

 

[UKMeterman]

Hi,
The spikes from lighting are been and gone in a few millonths of a second, faster than the RCD can move it's contacts. I would suggest having a chat with ABB techinical, they do a range of SPD devices and can also suggest RCDs that are not senstive to spikes. ABB Surge Protective Devices SPDs - Modular DIN Rail Products (Low Voltage Products and Systems)

 

[Octopus]

Thanks for the replies.
My concern is that if I do not have any type of rcd or spd (the current rcd is acting as a surge protector) then any spikes will travel to the main cu and trip any rcd there leaving us worse off than now. She will be stuck outside her gates whilst her freezer is defrosting!
I have never used an spd before, the one I referenced is £30 and looks like a solution that ticks all my boxes.

why is the RCD required?

 

[UNG]

Went to a property today where the lady is having problems with a 30mA rcd tripping during lightning. This is an upfront rcd protecting a small db in a large metal roofed garage which feeds 1)garage sockets, 2)garage lights, 3)electric gates and 4) fish pond equipment. It is the gates being disabled when the rcd trips that is the problem as she is in her 60's, recently widowed and past her gate jumping days.
I only had access to the garage where she left me installation certs mainly dated 2008 which showed a tt system with a Ze of 48 Ohms on one and 62 on another. On one of the certs it stated that this rcd had been removed but reinstated by the person doing the work. The house has had an extension 3-5 years ago and I assume the earthing was converted to pme as my Zrcd was .37Ohms, I was not left a cert covering this work. Obviously I have further investigations to do next week but it appears that the problem has been around for quite a few years and the earthing system is probably not relevant, the cpc had also been disconnected in the rcd enclosure. The rcd ramps at 21-24mA
I have been thinking along the lines of inserting an spd (Wilts controlgear SS40) between the rcd and the db to protect the rcd from what I assume to be large voltage spikes. My other options being replacing the t&e gate feed with swa so I could have an unprotected feed but this would allow spikes to pass to the house cu, or use four rcbo's and hope that the spikes are not originating from the gate circuit (which is a bit hit and miss for me).
I would be interested in how others have approached similar situations. App 18 of bgb shows spds on the load side of an rcd as I am thinking, I have never dealt with one before. My question is basically about the suitability of this spd, it's likely effectiveness and any other considerations there may be.
Have to go out shortly so there may be a delay in replying.

Thanks for the replies.
My concern is that if I do not have any type of rcd or spd (the current rcd is acting as a surge protector) then any spikes will travel to the main cu and trip any rcd there leaving us worse off than now. She will be stuck outside her gates whilst her freezer is defrosting!
I have never used an spd before, the one I referenced is £30 and looks like a solution that ticks all my boxes.

Before jumping to conclusions you need to take a step back trying to provide a solution without fully investigating the problem seems to be your problem here. I would suggest you approach this with a open mind and not be taken in by what the homeowner is telling you.
First off you need access to all of the installation and not just the garage, I don't know how many lightning storms you get in your location but this could just be a red herring, does this RCD tripping occur at at different times or the same / similar time of day, have you checked what leakage current is present on the CU the fish pond and electric gates from past experience can cause intermittent problems this is what I would be looking at, is there a fridge or freezer in the garage and has the auto defrost heater failed, is it water (heavy rain) getting into outdoor enclosures or underground joints. This is not an exhaustive list but a starting point to provoke some thought

Quite a bit to look at before you spend £30 and possibly not fix the problem