UK RCD Type A or Type S?

[SaajanB]

Hello!

I've been racking my brain this evening about some RCD selections. I've been doing some work for a solar installer, and they've asked me to do a battery storage setup, specifically with EPS for battery power.

I'm stuck on my RCD selection because basically, I'm going to shift 4x lighting circuits, the boiler, and a double socket into a seperate EPS CU loaded with RCBOs that is fed off the hybrid solar/battery inverter. My issue is selectivity and DC!

Basically the cable route means I can feed the solar inverter off and MCB, no protection required strictly speaking, then the EPS output routes back to the CU cupboard, again cable route means it doesn't have to protected, to the EPS CU where I 100% want to fit RCBOs as I don't want all the customer's lighting knocked out if one circuit has a fault.

Now, the regs don't specifically state we need RCD protection on the solar circuit, but I would like some, primarily to protect the equipment. So my first thought goes to a Type S 100mA RCD, but, Type S RCDs cannot detect DC currents!

So then my next thought is: let's just slap a normal Type A 100mA RCD in there and call it done, but then I'm worried that I'll get nuisance trips because there is no time delay hence not enough selectivity.

What would you guys do? Just leave the solar RCDless? settle for mediocre Type S protection? I'm racking my brain here!!!

Side question, why aren't they making Type A/S or S/A RCDs that are time delayed with the ability to detect DC currents as well???!!!!

 

[SaajanB]

Just to partially answer my own question, it appears Wylex do infact do a Type S, Type A RCD, the WRDMT100/2. According to the datasheet it has Type A leakage protection, so that might be my ticket. Only problem is, existing CU is a Hager so need to see if they do something along these lines.

 

[davesparks]

Now, the regs don't specifically state we need RCD protection on the solar circuit, but I would like some, primarily to protect the equipment.

What exactly do you want an RCD to protect the equipment from?

I can't see what kind of fault you are expecting which could damage the equipment and could be protected against by an RCD.

 

[SaajanB]

What exactly do you want an RCD to protect the equipment from?

I can't see what kind of fault you are expecting which could damage the equipment and could be protected against by an RCD.

To be honest I'd just prefer the peace of mind, at least the cable has some protection, and if the inverter starts going iffy it could potentially be helpful. Most installations I've done so far sit on a Type A RCBO.

 

[Risteard]

An S type (Selective) RCD is time-delayed. This is nothing to do with whether it's Type B, Type A, Type AC or whatever. So it can certainly be an S type with Type A RCD.

 

[davesparks]

To be honest I'd just prefer the peace of mind, at least the cable has some protection, and if the inverter starts going iffy it could potentially be helpful. Most installations I've done so far sit on a Type A RCBO.

Protection from what?

What kind of problem with the inverter is going to be helped by having an RCD on the circuit?