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Surge suppression without an earth

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Feb 3, 2022
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I am working on a subsea electrical installation. I have not earth but need to protect against surges from the generator. Feed is 400Vac, single phase, 3kW.

Most surge suppression units seen to bypass to earth, which is not possible.

Considering sing Transorb across power lines.

Any other suggetions?



Usually it´s this way:
* if you want to protect against overvoltage w.r.t. EARTH --> you need EARTH
* if you want to protect against overvoltage w.r.t. power lines --> you don´t need EARTH

Since you say you don´t have earth.. how could there be an overvoltage against EARTH?
I mean: You don´t have anything to refer to. (or in other words: how can you measure it?)


Surge suppression is all the usual ways

or if you have a filter...put some TVS's downstream of it to add better transient protection.

You can also have transient protection where you add a full wave bridge and a big HV capacitor after it...and a bleed resistor in pllel with the cap....the cap soaks up the transient.....also add a TVS in case its a really big transient..and tend to make the cap an x2 or x1 type cap

Ive seen people use absolutely massive inductive filters to give transient protection...the inductors were rated at more than 10 times the nominal current that would flow in that circuit.

The type of protection would depend more on the transient category to be suppressed; Generally speaking, in the absence of more detailed information about this EMI, I am particularly in favor of the idea of adding a switch breaker in series before the parallel surge suppressor itself, regardless of whether it meets general electric recommendations or not.

Thanks for you replies so far.

I'm not specified to meet any defined EMI/surge specification. However, I'm subsea but connected to a surface wave generator and which feeds our unit with an inverter. The wave generator itself could of course be struck by lightning etc, I have no indication of what protection they have. I'm just cautious as there is no access once deployed.

I was considering using a TVS to short the surge to neutral. I could use the case as earth but I'm not keen as when testing on the surface, the case will not be earthed.

I was looking at industrial surge suppressors but these require an earth.



we don´t know your exact situation.

Thus my thoughts (they may be fit to your application or not)

let´s consider a situation in a house.
You have a device with plastics case, no metal case, no EARTH.
It is isolated for standard situations.
But when a lighning happens it might be too much for the device´s isolation and an arc can happen:
Signal flow: lightning --> power lines --> device --> arc (across case) --> human (standing on concrete floor) --> earth.

Here a surge suppression against EARTH will limit the voltage at the device, prevent form arcing, saves life.

In your case, when a lightning happens, then install the "surge suppression to EARTH" on the surface = wave generaor side.


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