Inverter Earth/Neutral Bonding

[Dave_Beard]

Ok so i have read Gibbo's discussion from 2008 about how to identify the three main types of Inverter

using his idea of a 25 watt bulb wired across the outputs and earth and have found my inverter to be

of a type 1 ie no light on either live or neutral. So my question is now that i know it is safe to connect

earth and neutral were should this be done and how somewhere between the inverter plug top and

my RCD.

 

Thanks in advance

 

Dave Beard

[nicknorman]

Ok so i have read Gibbo's discussion from 2008 about how to identify the three main types of Inverter

using his idea of a 25 watt bulb wired across the outputs and earth and have found my inverter to be

of a type 1 ie no light on either live or neutral. So my question is now that i know it is safe to connect

earth and neutral were should this be done and how somewhere between the inverter plug top and

my RCD.

 

Thanks in advance

 

Dave Beard

Where: as you say anywhere between the inverter and the input to the consumer unit. How: well it depends on the particular hardware. I'd normally say at the inverter terminals but you mention inverter "plug top" so if this is a modest inverter with a 13A socket it will be easiest to do it within the consumer unit.

 

However, be careful if there is any other source of power such as shore power. Any EN connection on the boat mustn't be in circuit when on shore power. If you do have shore power, how do you switch between shore and inverter?

Edited June 2, 2015 by nicknorman

[Dave_Beard]

Hi Nicknorman i have a double pole switch before the rcd unit that switches between shore and inverter

but has a 0 isolator so no chance of trying to use both at the same time. I think i will just use the 230 volt

outlet on the inverter and wire that to my isolator but i am not sure whether the rcd will work as there is no earth

path.

[Arthur Brown]

RCDs need an earth wire and that the earth wire is connected ONCE to the supply neutral. Incoming mains is earth bonded, the inverter should be E-N bonded once somewhere near the inverter, but somewhere that doesn't use that bond when the shoreline mains is connected.

[nicknorman]

Hi Nicknorman i have a double pole switch before the rcd unit that switches between shore and inverter

but has a 0 isolator so no chance of trying to use both at the same time. I think i will just use the 230 volt

outlet on the inverter and wire that to my isolator but i am not sure whether the rcd will work as there is no earth

path.

 

So if I understand correctly the switch has a 1 - off - 2 configuration and switches both live and neutral? In which case you can put the NE link on that switch between the inverter input N terminal and earth. That way, when you switch to shore power the NE bond will be released. You're right, without an NE bond the RCD won't work when on inverter power.

[by'eck]

So if I understand correctly the switch has a 1 - off - 2 configuration and switches both live and neutral? In which case you can put the NE link on that switch between the inverter input N terminal and earth. That way, when you switch to shore power the NE bond will be released. You're right, without an NE bond the RCD won't work when on inverter power.

 

It will work but will have no trip reference. Consequently it won't provide the protection its fitted for.

 

If at all possible fit N/E strap at inverter. This won't leave any nasty surprises if the inverter is replaced in the future.

[nicknorman]

It will work but will have no trip reference. Consequently it won't provide the protection its fitted for.

 

Surely if it can't trip (which it can't do since, without an earth path, there can be no differential current between L and N) it can't be said to "work" - unless by "work" you mean remain on in perpetuity?

[Jess--]

if the earth line is bonded back to neutral at the inverter then ANY current using the earth line as a return to neutral instead of the neutral line passing through the RCD will make it trip.

 

if you think about it when a current is presented with 2 equal(ish) methods of returning to neutral around 50% will go via each route but only one passes through the rcd which will cause an imbalance at the rcd (since only 50% of the current is returning that way) this should make the rcd trip long before there is a dangerous amount of current returning via the earth line.

 

the most important thing to remember with RCD's is that all they are looking for is an imbalance between the current on the live and neutral connections.

Edited June 3, 2015 by Jess--

[Dave_Beard]

I have connected this inverter to my domestic battery and the plug top to my isolator switch

and it works fine including also the test switch on the rcd so i am happy that i am fully protected.

[GUMPY]

The test button on the rcd only tests the function of the rcd it does not indicate that it will trip corrcrtly under fault conditions.

Edited June 8, 2015 by Loddon

[Flyboy]

I have connected this inverter to my domestic battery and the plug top to my isolator switch

and it works fine including also the test switch on the rcd so i am happy that i am fully protected.

Have you checked your installation with a 3 light mains socket tester? If you have all 3 lights on you should be ok. If you don't then you are not N/E bonded & will indicate 'no earth' & the RCD will not protect you. As Lodden has said, the the test button on the RCD only tells you that it is working mechanically, it doesn't tell you if it will work with leakage live to earth.

[alan_fincher]

I have connected this inverter to my domestic battery and the plug top to my isolator switch

and it works fine including also the test switch on the rcd so i am happy that i am fully protected.

 

You are wrong to be confident based on that test alone, I'm afraid.

[smileypete]

Have you checked your installation with a 3 light mains socket tester? If you have all 3 lights on you should be ok. If you don't then you are not N/E bonded & will indicate 'no earth' & the RCD will not protect you. As Lodden has said, the the test button on the RCD only tells you that it is working mechanically, it doesn't tell you if it will work with leakage live to earth.

 

Just to add CPC have a free delivery offer at the moment, so a socket tester can be had for £2 delivered!

 

http://cpc.farnell.com/pro-elec/t203/plug-mains-tester/dp/PL1005205?ost=PL1005205

 

(Greenie given for mentioning the testers BTW...)

 

cheers, Pete.

~smpt~

Edited June 9, 2015 by smileypete

[Flyboy]

You make up a simple RCD tester to create a L/E fault condition. Wire a 8.6k ohms resistor from Live to Earth in a 13 amp plug. With the inverter on, the RCD should instantly trip when plugged in. If it doesn't, you have not got a E/N bond. Remove the plug immediately after the test.