RCD Protection on a PVinstall

[ian81]

Hi, can anyone help at all. Ive heard a few people say they dont put thier PV installs on an RCD, however am i correct in saying that under 17th edition everything should be RCD protected? If im being stupid please feel free to tell me incase ive missed something somewhere!!

Cheers in advance

 

[Worcester]

No you are not correct.

However you will need to specifically design out the requirement for an RCD otherwise you are likely to need one.

More info coming soon about this next point:

If you are using ANY make of TL inverter, you will not be able to install it in a situation where a 30mA RCD is required.

So if you MUST have a 30mA RCD, then you will almost certainly have to install a transformed inverter.

 

[ian81]

In somecases weve used a garage unit with a 100mA rcd and ran armoured cable because weve used a sunnyboy 4000tl. It was just someone said to me that the PV course theyd done they was told to not install the system on an RCD.

 

[Worcester]

If your 100mA RCD that you installed is a Type A then you may just as well not have installed it at all.

If the Array has any DC leakage at all (over 25 years a fault could develop) then the RCD will not trip even under 300mA of AC leakage.

 

[MorganPVI]

Under DC fault conditions any RCD apart from a type B will be useless, it could become saturated and may not trip. If you need to protect your AC circuit using an RCD then as Worcester says design out the need for a RCD. You could use a Type B 30ma, but you run the risk of nuisance tripping.

Any installer / designer who relys on the inverters having inbuilt type B protection could be leaving themselves wide open in the event of DC faults.

 

[Tiberius]

Its also highly unlikely that the AC cable will be ran anywhere that requires RCD protection that reg states.

 

[BruceB]

Its also highly unlikely that the AC cable will be ran anywhere that requires RCD protection that reg states.

Agreed for most domestic situations. But if TT or agricultural then regs require a rcd whatever routing or cable type.

 

[SibertSolar]

Many valid points here, I think a definitive statement that might help clarify some of the above might be useful for those on this forum reading this, and other RCD threads. I can provide technical/supporting info if that is of any use?

 

[Graeme Harrold]

Just look at many "No Trip" Loop Testers, they use DC to latch the RCD while the test is being conducted.............say no more.....

 

[GaryM]

Just look at many "No Trip" Loop Testers, they use DC to latch the RCD while the test is being conducted.............say no more.....

I thought they just put a limit on test current to 15mA so it won't trip a 30mA RCD.

 

[coomers]

if its a tt system whatever the inverter 100ma required for surface wiring 30ma for cables burried within fabric of building unless protected by swa or steel etc
tncs or tns no rcd required for surface wiring but as above again for burried.

 

[SolarCity]

I don't think the 15mA test current testers were very popular as that didn't correctly test the integrity of the system. I seem to remember my tester using DC to overcome problem tripping during testing. Although now I'm struggling to work it out in my head.

 

[Worcester]

TL inverter on a TT system then will need a Type B RCD.

Andy - we could do with that decision tree!

 

[GaryM]

I don't think the 15mA test current testers were very popular as that didn't correctly test the integrity of the system. I seem to remember my tester using DC to overcome problem tripping during testing. Although now I'm struggling to work it out in my head.

I use a Megger 1552 which is possibly one of the most popular multifunction testers available. That uses a test current of 15mA to avoid tripping 30mA RCD's on the low current loop (no trip) setting.

 

[edexlab]

Type A 100mA Rcds can be used on Inverters which by construction/ design are not capable of feeding in Dc injection currents to the grid Reg 712.411.3.2.1.2 identical wording to this in some Inverter manufacturers info
so check the manufacturers instructions for example SMA 4000tl Type A Rcd can be used