Fused Neutral?

[Ticketmaster]

I am aware that a fused neutral is against the NEC in the US and not approved in Europe. The ostensible reason is that if you have both the line and neutral fused with the same amperage fuse, get a short, and the neutral fuse blows first, it will leave the juice running into the affected circuit. It could even leave a metal appliance case energized. It is potentially dangerous. You are not supposed to do this. I know this. But.

Intuitively, it seems that if you had both the line and neutral fused between the meter and the main panel (which contains proper circuit breakers) it could offer lightening protection. If there was a direct strike on the neutal line on the pole, wouldn't it blow the neutral fuse before burning up all the circuit boards in the various appliances around the house?

I have a Schneider SPD 225, but is it a class 2 MOV device rated at only 15kV. It will not provide protection against a direct line strike close to the house. Will a fuse offer any such protection? And again, I assuming a direct strike to the neutral.

Further, if you have the neutral fused only on the incoming line, and it blew, the whole house would be down. If the main breaker was open and the grid wasn't down, you would know immediately it was the fuse and remedy the situation. It seems less dangerous that having a single circuit with a neutral fused (as in the old days), where one might not be aware that the neutral fuse had blown.

[Crossy]

NEVER, EVER, EVER fuse the neutral!

There are reasons that it's not permitted by the major electrical codes and not just the ones you cite (although an apparently dead system where every conductor is live is a pretty good reason). Why not analyse what happens in an unbalanced 3-phase system when the neutral goes open?

Also, since all new installations are supposed to be MEN (PME) with a link between N and E if your neutral fuse opens all your 'earthed' metalwork will become potentially lethal (how lethal depends upon how good your earth rod is).

As for lightning protection, your electronics will fail long before a fuse opens and even an open fuse will provide no barrier to a direct strike. The strike has already come through 10,000 feet of air, an additional 1" in your fuse will not even be noticed.

TBH there is pretty well nothing that will save your kit against a direct hit, your 15kA device will provide pretty good protection from a close hit (although a bigger one would be better, ours is 60kA), add some quality plug-in arrestors to your delicate gear and you're as well protected as it's possible to be without breaking the bank.

[Ticketmaster]

NEVER, EVER, EVER fuse the neutral!

There are reasons that it's not permitted by the major electrical codes and not just the ones you cite (although an apparently dead system where every conductor is live is a pretty good reason). Why not analyse what happens in an unbalanced 3-phase system when the neutral goes open?

Also, since all new installations are supposed to be MEN (PME) with a link between N and E if your neutral fuse opens all your 'earthed' metalwork will become potentially lethal (how lethal depends upon how good your earth rod is).

As for lightning protection, your electronics will fail long before a fuse opens and even an open fuse will provide no barrier to a direct strike. The strike has already come through 10,000 feet of air, an additional 1" in your fuse will not even be noticed.

TBH there is pretty well nothing that will save your kit against a direct hit, your 15kA device will provide pretty good protection from a close hit (although a bigger one would be better, ours is 60kA), add some quality plug-in arrestors to your delicate gear and you're as well protected as it's possible to be without breaking the bank.

Can you tell me where you got your 60 kA device and what is the brand and model? I have searched high and low and could only find them in Australia.

As to the MEN link, I have read all your stuff on it and done a lot of research, but am still a novice. May I ask, is there any time in Thailand (way out in a village with a 50kV transformer and single phase) that I should NOT use a MEN link?

Edited March 21, 2013 by Ticketmaster

[Crossy]

Can you tell me where you got your 60 kA device and what is the brand and model? I have searched high and low and could only find them in Australia.

It's actually one of these http://www.amazon.co.uk/Phase-Power-Surge-Arrester-Protector/dp/B007PPHBDW but obtained in Shanghai (along with some spare cartridges) when I was there on business.

[Crossy]

As to the MEN link, I have read all your stuff on it and done a lot of research, but am still a novice. May I ask, is there any time in Thailand (way out in a village with a 50kV transformer and single phase) that I should NOT use a MEN link?

My usual advice regarding MEN is that you should NOT install a N-E link unless you KNOW that MEN is implemented in your area.

The usual clue is the neutral being grounded every third pole or so.

[Ticketmaster]

Thanks. Seems I saw something on your site about the local folks having to implement it first. Easy enough to check the grounded neutral on poles. I think I have seen that here. I'll take a walk tonight.