Fusing the mains

[zappedagain]

OH, my three-phase is rusty...

In North America, we typically get 120VAC off one phase, with one side referred to as hot (line) and the other as neutral (reference, typically held close to earth ground by the power provider). A single fuse gets installed on the hot side. If we want 220 VAC, we use two phases, so each 120VAC has a common reference of the earth ground and adds to 207VAC (close enough for horseshoes), and each phase gets fused.

In Europe (or most of the rest of the world), you typically have 240 VAC. Is that set up as a line (hot) and neutral, or as two phases?

And on to my real question. When running off the mains in Europe, do I need to fuse both wires at the power inlet? I have seen IEC320 power entry modules with a single fuse and a double fuse; is this why?

 

[zeusfaber]

230V single phase (plus or minus enough to accomodate UK's 240 and everybody else's 220 within a common spec) is phase to grounded neutral. You fuse the live, but not the neutral.

If you use all three phases, you need to fuse all three of the phase lives (but still not the neutral), and get 415ish volts between phases.

I can't think of anywhere in this part of the world where we use just two of the three phases.

A.

 

[dpc]

The 240 V power in the US is not two phase. Just center-tapped single-phase.

 

[zappedagain]

Thank you. It is coming back to me slowly.

On a related topic, a colleague suggested fusing the live and the neutral, in case someone manages to plug into the mains backwards and swaps live and neutral. I'm thinking that is a bad thing if the real neutral fuse blows first. Is that good practice or bad practice?

 

[itsmoked]

Very bad. Never fuse the neutral.. Many nasty ramifications.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

Agreed - fusing a neutral conductor is generally a code violation.

 

[zappedagain]

That's what I thought. Thanks for the confirmation.

Z

 

[cranky108]

So Europe's distribution secondary is Wye grounded?

Interesting, because in some South American countries there system is delta 240vac. Where each phase is fused, and there is no neutral (good thing as many people there seem to be confused about electricity).

 

[ScottyUK]

Yes, the majority of Europe if not all of it uses a grounded neutral. Certainly the western European countries use a grounded neutral.

A neutral can be switched using a ganged two-pole switch or circuit breaker, but not two single pole switches or breakers.


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If we learn from our mistakes I'm getting a great education!

 

[bogeyman]

We do use single phase 415/440v (2 of 3 phases) in the UK within machine control cabinets to power low voltage kit via transformers, usualy for lower power stuff like panel lamps and relays.
This is done to accomodate delta connected power inputs which reduce the power cable count to 3 + ground.

 

[zeusfaber]

Bogeyman:

There's a thing I didn't know. Thanks.

A.

 

[ScottyUK]

It's common in MCC starter buckets where the neutral connection isn't brought into the starter. Needs careful consideration to make sure fault ratings are not exceeded when using small MCBs to protect control wiring.



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If we learn from our mistakes I'm getting a great education!