138/240Y System

[Cookie]

How would everyone feel about a 240Y system in a building with everything connected Line-Line?

I personally like (want) this system. No TN-C, TN-C-S vs TN-S debate. No earthing/bonding debates of how to keep the neutrals separate in a multi source or generator system. No fire or shock risk from a broken PEN/MEN. No need to keep track of live and neutral in a circuit.

Just asking curious.

 

[Lucien Nunes]

This was quite common in mainland Europe at one time but AFAIK never used in the UK. It requires double-pole fusing and switching for single-phase loads, which we do not generally adopt, and reduces the overall system voltage by sqrt(3) meaning more copper is needed for the same power. If you are not going to use the neutral then there's no real point distributing that, so you might as well call it a delta supply. Ground a centre-tap on one winding and you've got the US system, which is ingenious and versatile but through UK eyes, when we're used to working with 400V, the amount of current you need to do anything useful seems terribly cumbersome.

You seem to be trying to solve a problem that doesn't exist. If you don't accept the risk of a MEN / CNE, then make it TN-S and use 5 wires everywhere. You'll still use less copper than lowering the line-line voltage to 240V and getting rid of the neutral.

 

[Cookie]

But there is a point in distributing it (as a PE) in an effort to create a low impedance path to facilitate the operation of over current devices.

TN-S still has the risk of open neutral.

But I will agree with you, the copper will be greater. Perhaps double is not more in some cases.

 

[Lucien Nunes]

Sure, running single-phase loads line-line eliminates the possibility of damage by overvoltage from a broken neutral. I've seen plenty of that in my line of work. But in TN-S the impact is an economic one, not one of shock protection. Which is cheaper, replacing stuff broken by overvoltage or running heavier cables? There is a possible incidental benefit of imposing double-pole OCPD and switching on things out of necessity, although that could be introduced in regulations even for 1P+N+E.

The case for / against PME on grounds of shock risk is separate.

 

[Cookie]

Well, if you are going to damage equipment, you will also shock on a TN-C-S.

And switches don't have to be double pole, only the over current and disconnection (for service) devices.

 

[Cookie]

And I don't mean to be a hard head lol, but in the US this system would actually save copper. And fix so many stray current/voltage issues.

 

[Sisyphus]

Dealing with MEN's is often a power quality issue , the NEC doctrine only acknowledges Mr Kirchhoff when convenient to do so. ~S~

 

[Cookie]

Well, I agree, neutral current on all the structural steal.

 

[davesparks]

Well, if you are going to damage equipment, you will also shock on a TN-C-S.

And switches don't have to be double pole, only the over current and disconnection (for service) devices.

In the UK they would have to be DP switches to satisfy the regulations.

 

[Cookie]

Even for switching off a light? Can't see the reasoning.

 

[Bobster]

Because you would still have a dangerously high potential to earth at the lamp fitting.

So mr.homeowner could inadvertently touch something lethal changing a blown lamp.

 

[Cookie]

Only if he or she were to stick their fingers in the Bayonet.

 

[Bobster]

Only if he or she were to stick their fingers in the Bayonet.

Exactly, not entirely unforeseeable. .

 

[davesparks]

Even for switching off a light? Can't see the reasoning.

Because lightswitches are the means of isolation for each light fitting therefore need to isolate all conductors.

 

[Cookie]

You guys have a BS7671 code section?