A question about neutral-earth bonding

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william asked Feb 17, '24

A question about neutral-earth bonding

A question about neutral-earth bonding for a Multiplus 24/3000/70-16 off-grid system, with Sunny Boy 2500HF-30 solar inverter and generator backup. In the UK.

I have recently taken over this installation which was originally installed (in 2015) with a N-E bond in the consumer unit (elsewhere named breaker panel, distribution board etc), even though the Multiplus has an internal N-E bond when there is no AC input. When AC input is present (in our system from a generator), the Multiplus N-E bond is opened and the system uses the N-E bond at the generator. The bond in the CU was later removed (probably around 2019), not by the original installer and not by me.

My understanding is that there should not be a N-E bond in the consumer unit when the Multiplus (or our generator) has it. I have asked the original installer why the N-E bond in the CU was made, the reply was 'I don’t think the sunny Boy will work without it as it shows a PE fault'. Well, the Sunny Boy doesn't show a PE fault and it works fine.

Thanks for reading this far, here are my questions:

1. Does anyone have any experience of a PE fault using Sunny Boy inverters?

2. Are there any circumstances where a CU should have a N-E bond in this kind of installation?

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kevgermany ♦♦ commented · Feb 18 at 04:56 AM

Multiple N/E bonds create earth loops. You must only have one active. Having one in the consumer unit will give a ground loop at times.

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Answer 1 · 2024-02-17T14:59:33Z

regman54 answered · Feb 17 at 02:59 PM

If memory serves me correctly here in Canada (and likely the US as well) only one earth ground is allowed. My gasoline powered inverter generator for example has a floating neutral. If an earth ground is made to the generator the RVs own Electrical Management System will block the power supply from the generator or a faulty electrical outlet until the generator's earth ground is removed. Having said all that I would play it safe and contact a local electrician and ask them

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Answer 2 · 2024-05-11T13:31:55Z

offgridvoltage answered · May 11 at 01:31 PM

My understanding is that there should always be only one(1) E/N bond and that bond should always be at the source of power. i.e. Whilst in 'inverting mode' this bond will come from the source of power, being your multiplus. Whilst the Generator is applying power to your Multiplus, it's ground relay will break the E/N bond, so this E/N bond should then come from your generator as the source of power. Likewise, when connected to shore power, the Multiplus relay will again break the E/N bond and that bond should then come from your consumer unit (or fuse box / meter box as we call them in Oz) Here is an awesome source of info regarding this big and devisive topic >>

https://diysolarforum.com/resources/grounding-made-simpler-part-1-ac-houshold-grounding.157/

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