120V through PV Earth??

[Kevin]

Hi,

I'm currently doing a re-wire on a property that has already had PV installed. I changed the consumer unit today, and whilst re-arranging the MET, noticed that the main earth coming from the PV consumer unit sparked. I put my Fluke between the PV main earth and the MET and found I have 120V on the earth coming from the PV CU. This lowers to 32V when I switch the PV isolator off. I tested another identical property two doors down and had exactly the same readings from that PV system too. I believe it's a Suunyboy inverter with isolating transformer.

Any ideas what this may be?

Many thanks

Kevin

 

[Gavin A]

could it be capacitors discharging?

all seems very odd, can't say I've ever come across it, so would suggest someone's done something wrong.

check if there's an earth cable from the roof, check if either dc terminal is bonded to earth, check if they've wired the neutral to the earth terminal inside the inverter - those inverters do have slightly odd arrangements for wiring the AC cable in, so actually that'd be my guess.

 

[Kevin]

Cheers Gavin, I'll take a closer look today.

 

[SolarCity]

Let us know what you find. It sounds like an interesting one.

 

[Kevin]

OK, I've had a closer look and still none the wiser. I isolated the panels but left the inverter on, and still got the 120V on the earth. I've opened up the PV consumer unit, both AC rotary isolators and the DC rotary isolator, the AC connector at the inverter and the inverter itself, all are ok, with no reverse polarity, and no earth/neutral problems. There is no bonding to the array itself, but I'm assuming this isn't an issue as the inverter has an isolating transformer. I have now tested three properties in the area, and all three have 120V on the earth?

Not sure where to go from here. Do the MCS have a helpline or possibly Sunnyboy?

many thanks

Kevin

 

[snowhead]

Not sure where to go from here.

Kevin

Contact the original installer or the P.V owner if it's rent a Roof.

 

[ExtremePV]

Whats the model number of the inverter?

 

[Gavin A]

Not sure where to go from here. Do the MCS have a helpline or possibly Sunnyboy?

many thanks

Kevin

lol - yeah, I'd love to hear what MCS office monkeys came up with.

They'd probably try to persuade you that only MCS members should work with solar at all or something......

I'm now wondering how you know it's a problem with the solar and not 120V on the local suppliers earth? Seems very odd that there'd be the exact same voltage and issue with 3 solar units. Were they all exactly the same systems installed by the same company?

What's the ampage on this earth leakage / whatever it is? If it's a few miliamps then it's a bit less concerning / more understandable.

Can you tell us the make and model of inverter & the make model and number of the panels?

 

[Kevin]

lol - yeah, I'd love to hear what MCS office monkeys came up with.

They'd probably try to persuade you that only MCS members should work with solar at all or something......

I'm now wondering how you know it's a problem with the solar and not 120V on the local suppliers earth? Seems very odd that there'd be the exact same voltage and issue with 3 solar units. Were they all exactly the same systems installed by the same company?

What's the ampage on this earth leakage / whatever it is? If it's a few miliamps then it's a bit less concerning / more understandable.

Can you tell us the make and model of inverter & the make model and number of the panels?

Well, my company are members of the MCS, although we didn't do these installs. I'll check the model number of the inverter today. These three systems are the same, with the same inverters, possibly installed by the same company (I know two were, not sure of the third)

I'd though of the possibility of a problem existing on the incomer, however I have disconnected the main earth, and then placed my meter between this and the MET and I get nothing. Also tried disconnected main earth to the main consumer unit and nothing here either. It is only when I disconnect the main earth to the PV board and go between this and the MET.

Will get the inverter and panel details today.

Cheers

 

[SolarCity]

Are you 100% sure that the frames are not bonded? Could they be bonded to an earth rod?

 

[Kevin]

OK, the inverter is a Sunnyboy SB3000HF-30. Not sure of the make of panel though. Positive that the array isn't bonded though.

Although I've got 120V on the earth, I've put the clamp meter on it, and it's less than 0.01 Amps. We've contacted the Housing Association whose properties they are, and left the ball in their court now.

Many thanks for the replies.

 

[Marvo]

We've had a few confusing voltage measurements to earth before on the forum and I'd still maintain that any voltage measurement of 120v (or 32v for that matter) WRT earth is a meaningless measurement without context, which would include the input resistance (read impedance) of the actual tester. If you're seeing stray voltages WRT earth on any circuit I'd suggest verifying them with an analogue tester first. If the voltage appears to be much lower with an analogue tester then bond the guilty circuit to earth (via a known resistance if necessary) and take a leakage reading in milliamps (or more likely microamps). Bottom line is if you use a tester with a high enough input impedance you'll be able to measure 120v just about between any two objects or points. There's a very good chance you're seeing a coupled or induced voltage either through proximity or maybe even by RF signals such as local WiFi for example.

*Edit*
Inverters of any sort are also notorious for standing leakage, I imagine PV inverters are no exception. The Earth is functional as well as protective so I wouldn't worry about a milliamp or two of leakage current.

 

[sambotc]

I posted about this on a fronius inverter a few years ago. I checked with fronius and their reply,was that it was normal and safe as 0 amps.

http://www.electriciansforums.co.uk...ius-igtl-3-0-dc-down-ac-issue.html#post445803

 

[Gavin A]

thing is, if there's 0amps then why is it sparking?

 

[sambotc]

Same reason a stun gun sparks i guess ? I dunno there has to be some current there but minimal? Not really sure. That is of course, if it is the same problem.