Electrical question: Circuit breaker in panel

[kckku]

I am getting a small machine from Europe. For whatever reason there isn't a circuit breaker after the disconnect switch for the electrical panel. The connection goes directly to the 120 VAC to 24 VDC power supply. I have never seen this before. Is this even allowed? Is there some weird case in Europe where this is allowed?

The machine hasn't shipped yet and I am going to call them out for this. I don't know what's going on here.

 

[Saffa]

Looks like they are expecting you to supply this with 115V, 16A max from a circuit breaker in the upstream switchboard. Since there is only a 24VDC PSU being fed through the disconnect, they have no need for any additional breakers inside the panel;

Of course maybe the regulations where you are wouldn't allow this, but it would be perfectly legal here. The only thing we typically wouldn't do is break the neutral through the disconnect.

 

[kckku]

Looks like they are expecting you to supply this with 115V, 16A max from a circuit breaker in the upstream switchboard. Since there is only a 24VDC PSU being fed through the disconnect, they have no need for any additional breakers inside the panel;

Of course maybe the regulations where you are wouldn't allow this, but it would be perfectly legal here. The only thing we typically wouldn't do is break the neutral through the disconnect.

I see what you are saying with the upstream breaker. Thanks for the quick reply.

It would still be annoying to have to go find the main switchboard panel to reset. We probably also have to wait for the plant's electrician. Probably cheaper just to install a circuit breaker in this machine's panel.

 

[Jim3846]

I agree with the neutral should not be disconnected thru the disconnect.

Best just install a breaker in the unit, asbuilt it with a breaker. Tell them next time provide a breaker in their design.

 

[kckku]

Looks like they are expecting you to supply this with 115V, 16A max from a circuit breaker in the upstream switchboard. Since there is only a 24VDC PSU being fed through the disconnect, they have no need for any additional breakers inside the panel;

Of course maybe the regulations where you are wouldn't allow this, but it would be perfectly legal here. The only thing we typically wouldn't do is break the neutral through the disconnect.

I agree with the neutral should not be disconnected thru the disconnect.

Best just install a breaker in the unit, asbuilt it with a breaker. Tell them next time provide a breaker in their design.

I can tell them to add a circuit breaker. They haven't shipped the machine yet. If it won't pass inspection here in Canada as is then they will have to do this at no cost. I just want to make sure I know what I am talking about before making this request.

Thanks.

 

[kamenges]

Originally posted by Jim3846:

I agree with the neutral should not be disconnected thru the disconnect.

I have seen this both ways. We sent a machine to the UK a few years back that required the neutral to be disconnected along with the (in this case) 3-phase supply. I read into the rationale on this and it sorta-kinda made sense. The neutral can be consider a current carrying conductor and often is in 400V systems where 240 can be derived directly from the main feed. When the disconnect is in the off position the implication is that all current carrying conductors are isolated. In most cases the neutral wire will not run directly back to the supply neutral but will pass through a panelboard or other enclosure somewhere. So what if something happens to the integrity of the neutral conductor running from the panelboard to the source AND another machine fed from that panelboard derives it's 240V between a phase and neutral? Suddenly the neutral that we thought is at 0V potential is no longer at 0V potential.

I don't think a supplier needs to provide overcurrent protection at the supply terminals to specifically meet any code. However, I think there needs to be a local disconnecting means (whatever local means), which in North America often includes the supply overcurrent protection.

Keith

 

[janner_10]

Yes an MCB should be fitted prior to the power supply on good practise alone.

Also we switch the neutral here as it's classed as a live conductor.

 

[Rob...]

Also a obvious note to add, the neutral needs to be late break, early make. IE the 3 line phases need to disconnect first, an then the neutral. An on re energizing the neutral needs to be made first.

 

[JesperMP]

It is quite normal that there is no common circuit breaker in the start of the panel. The panel will have a rated short circuit current which the external supply must be limited to.

It is probable that the cabinet supplier expect that there is a circuit breaker upstream that takes care of the short circuit protection of the panel, and the entire panel is then rated for the short circuit current of the assumed circuit breaker.
Is there a sign inside or outside stating the electrical information of the cabinet ?
There should be information regarding rated voltage, rated current I_N, rated conditional short circuit current I_CC, rated peak withstand current I_PK, and more.
This information should be enough for you to select the protection in front of the panel.

Inside a control cabinet you usually have devices to bring the short circuit current further down, i.e. fuses, circuit breakers, transformers.
I have not seen a 24V power supply used as a current limiting device before in this sense, but thinking about it, I can see how it could be possible. The power supply specs must state this clearly.

 

[janner_10]

Also a obvious note to add, the neutral needs to be late break, early make. IE the 3 line phases need to disconnect first, an then the neutral. An on re energizing the neutral needs to be made first.

Not heard of the one before.

 

[I_Automation]

Basically it is coming with a 115V electric plug (or not - you add one) expecting the outlet to be protected.



How many 120V devices have you seen with a circuit breaker or fuse? (not counting Christmas light strings) Coffee makers, microwaves, electric frying pans, TV's, blenders, mixers, printers (photocopiers usually do), vacuum cleaners, refrigerators, washers, gas dryers, gas stoves, etc.

 

[AustralIan]

In the UK, they have a fuse built into every plug of every domestic appliance. The fuse is supposed to be sized to the appliance. Brilliant.