Best location for consumer unit (renogy gear - advice needed)

[roadtripper]

Those are double pole single phase it im not mistaken. In other words, no good if have a reverse polarity supply as in some Euro campsites.

Double pole is what you want (2 poles on the switch so disconnecting both Line and Neutral)

Most of these devices will be single pole so only disconnecting Line with the expectation that the main switch/RCD in the Consumer Unit is double pole to provide full isolation.

Reverse polarity is a risk as it means that the side of the circuit wired as Neutral is actually connected to Line meaning it will be at mains voltage even when apparently off. That means a single pole RCD like device would not disconnect that if it tripped.

However you arrange your EHU supply you must always have a double pole RCD either as part of the main switch (which is most common) or as part of the RCBO (which are much harder to find) because there is always the risk of reverse polarity in temporary installations.

I'd very strongly recommend testing the polarity each time with a socket top tester or one built in as it's still dangerous as the switches will be on the wrong side of the circuits.

 

[Skyliner33]

Double pole is what you want (2 poles on the switch so disconnecting both Line and Neutral)

Most of these devices will be single pole so only disconnecting Line with the expectation that the main switch/RCD in the Consumer Unit is double pole to provide full isolation.

Reverse polarity is a risk as it means that the side of the circuit wired as Neutral is actually connected to Line meaning it will be at mains voltage even when apparently off. That means a single pole RCD like device would not disconnect that if it tripped.

However you arrange your EHU supply you must always have a double pole RCD either as part of the main switch (which is most common) or as part of the RCBO (which are much harder to find) because there is always the risk of reverse polarity in temporary installations.

I'd very strongly recommend testing the polarity each time with a socket top tester or one built in as it's still dangerous as the switches will be on the wrong side of the circuits.

Just re read my post and realised I shouldn't post in such a rush early in the morning.

I believe that this in the link posted are 1P+N even though they are listed as double pole.

 

[drinfinity]

Just re read my post and realised I shouldn't post in such a rush early in the morning.

I believe that this in the link posted are 1P+N even though they are listed as double pole.

Thanks, @roadtripper and @Skyliner33 are right. I’ve just tested the RCBOs, and indeed they do break only the live feed, not the neutral. I’ll change them for something that really is double pole rather than claiming to be.

 

[drinfinity]

Found some Wylex alternatives, which not only claim to be double pole in the description, there is a circuit diagram printed on showing double pole switching.

 

[Skyliner33]

Found some Wylex alternatives, which not only claim to be double pole in the description, there is a circuit diagram printed on showing double pole switching.

View attachment 246524

Check the data sheet on that. I am sure it’s 1P+N.

 

[drinfinity]

According to the data sheet, they certainly are switching the neutral.

Inside the device the conductors pass through a loop, and any difference in current flowing in to out creates a net magnetic field which can be detected to then trip the switches.

So as I understand it, when there is a difference in current flowing through L and N (a leak to earth) system will trip, disconnecting both conductors. If the L and N supply were reversed, then again whenever there is a difference in current flowing, system will trip.

Then there is overcurrent protection. Here the data sheet is less informative. However, assuming that the same amount of current comes out as goes in, and that it is AC, then measuring overcurrent on one line would be independent of which is L and N. There can’t be an overcurrent situation on N but not L without a difference in current between the two, which would trip the RCB.

I’m a chemist rather than an electrician, but I’m trying to get my head around if there is any failure mode that the Wylex versions would not protect (information sheet below).

Ultimate goal is to have a protected installation, against earth leakage and overcurrent, regardless of which way round the shore supply is wired, and in a smaller box than the standard consumer unit.

https://www.farnell.com/datasheets/2672189.pdf

 

[roadtripper]

So first thing - this is not in any way detecting leaks to earth - that's an ELCB and is now not recommended as there are many faults that don't present as leaks to Protective Earth in the wiring.

An RCD senses imbalance of current between Line and Neutral because if they are not even current is going somewhere it shouldn't regardless of reason. The only reason we talk about earthing and grounding is that if there is a fault where the Line conductor touches metal we want that metal to solidly bonded to the Protective Earth and that to be a current path that is very low resistance so current flows easily - that sounds odd but you actually want a fault current to be large as that is what results in reliable tripping. So good path to earth + protective device = fast reaction time so more safety.

Those devices explicitly talk about disconnecting the Neutral to help with testing a CU - and that's actually a very good idea. The datasheet a bit later in is confusing as there are 2 items of protection in this device - RCD and Over current - and it's not clear which one they mean. Most likely what they mean, seeing as the list both the RCBO and MCB version, is that there is no over current protection on the Neutral because, as you say, they must be monitoring both Line and Neutral in the RCD side of the RCBO.

So as I read it that gives the same protection as an MCB fed from a dual pole RCD main switch (the normal layout) - there may be edged cases that doesn't protect against but it would apply to both (surge and arc faults come to mind)

Caveat is I'm a physicist by training and done a fair bit of event electrical work but I'm not a fully qualified electrician and I don't have a copy of the wiring regs to hand.

If it was me I'd set up a very careful test rig that brought all three conductors (L, N, PE) out to something like a choc block bolted to something safe and then use a high current resistor in electrically safe pliers with a good glove to briefly connect L to PE and N to PE to verify the RCD protection. But I absolutely do not recommend that unless you appreciate how to do that safely.

 

[Skyliner33]

According to the data sheet, they certainly are switching the neutral.

Inside the device the conductors pass through a loop, and any difference in current flowing in to out creates a net magnetic field which can be detected to then trip the switches.

So as I understand it, when there is a difference in current flowing through L and N (a leak to earth) system will trip, disconnecting both conductors. If the L and N supply were reversed, then again whenever there is a difference in current flowing, system will trip.

Then there is overcurrent protection. Here the data sheet is less informative. However, assuming that the same amount of current comes out as goes in, and that it is AC, then measuring overcurrent on one line would be independent of which is L and N. There can’t be an overcurrent situation on N but not L without a difference in current between the two, which would trip the RCB.

I’m a chemist rather than an electrician, but I’m trying to get my head around if there is any failure mode that the Wylex versions would not protect (information sheet below).

Ultimate goal is to have a protected installation, against earth leakage and overcurrent, regardless of which way round the shore supply is wired, and in a smaller box than the standard consumer unit.

https://www.farnell.com/datasheets/2672189.pdf

I agree, the 1P+N means that it will switch both the line and the neutral.

However only the line is monitored, so in a reverse polarity situation an overcurrent will not trip. Watch that video someone posted earlier in this thread. It explains the difference between a 1P+N and a DP. I can not find any 'slim' versions that are DP.
Not had time to look properly, but at first glance this:

https://www.cef.co.uk/catalogue/products/4946302-16a-double-pole-2-module-c-curve-10ka-30ma-type-a-mini-rcbo

 

[Skyliner33]

@roadtripper beat me too it again.

 

[drinfinity]

I watched the video, but I still don’t get the ‘how’. RCBO is connected only to live and neutral lines. In a fault situation, some current is leaking out to earth, so there is less current on the return line than the supply. It detects this difference by measuring the net magnetic field.

How is it possible to measure only one conductor? Suppose I feed a live current into the neutral input of the RCBO, and some of it leaks to earth. There is now less current on the other side of the device, and so a difference. Why would the same physics not apply, and again trip the device?

 

[drinfinity]

For the overcurrent fault, again, how can we have overcurrent only on one side of an AC circuit, without tripping the RCB? The video was about designs for EV charging, where there could be a DC component, and critically energy coming back in the opposite direction (hence the bidirectional label on the linked device from CEF).

I’m a chemist rather than an electrician, but I do know my way round an electron. I’m trying to get to a consistent understandings of what’s going on inside the black box. (OK it’s a white box…)

 

[roadtripper]

I watched the video, but I still don’t get the ‘how’. RCBO is connected only to live and neutral lines. In a fault situation, some current is leaking out to earth, so there is less current on the return line than the supply. It detects this difference by measuring the net magnetic field.

How is it possible to measure only one conductor? Suppose I feed a live current into the neutral input of the RCBO, and some of it leaks to earth. There is now less current on the other side of the device, and so a difference. Why would the same physics not apply, and again trip the device?

Again don't focus on "earth" and focus on "current imbalance" - both myself and @Skyliner33 agree with you that the RCD element must be monitoring both and therefore should trip either way

 

[drinfinity]

Again don't focus on "earth" and focus on "current imbalance" - both myself and @Skyliner33 agree with you that the RCD element must be monitoring both and therefore should trip either way

Agreed there. On Overcurrent, how can we monitor only one line?

 

[roadtripper]

OK - a bit of digging and I think this is just a terminology confusion.

"1P + N" is a way of describing a single phase protective device when compared to a "3P + N" three phase device - and in the three phase device it is definitely possible to have situations were the individual phases are not overloaded but the common neutral is.

For the devices we are talking about used in the way you are talking about "1P+N" == "DP" for all effective cases.

The cases where they would not be equivalent is in some specialist supplies such as a Centre Tapped Earth transformer and neither "pole" is wired to neutral.

 

[drinfinity]

OK - a bit of digging and I think this is just a terminology confusion.

"1P + N" is a way of describing a single phase protective device when compared to a "3P + N" three phase device - and in the three phase device it is definitely possible to have situations were the individual phases are not overloaded but the common neutral is.

For the devices we are talking about used in the way you are talking about "1P+N" == "DP" for all effective cases.

The cases where they would not be equivalent is in some specialist supplies such as a Centre Tapped Earth transformer and neither "pole" is wired to neutral.

Thanks - that makes sense, much appreciated.

 

[Skyliner33]

OK - a bit of digging and I think this is just a terminology confusion.

"1P + N" is a way of describing a single phase protective device when compared to a "3P + N" three phase device - and in the three phase device it is definitely possible to have situations were the individual phases are not overloaded but the common neutral is.

For the devices we are talking about used in the way you are talking about "1P+N" == "DP" for all effective cases.

The cases where they would not be equivalent is in some specialist supplies such as a Centre Tapped Earth transformer and neither "pole" is wired to neutral.

From what I heave read, they are not the same, ie 1P + N does not equal (cant find the sign) DP.
From my research it means the breaker (1P+N) will disconnect both poles however the overcurrent sensing is only performed on the Line. Therefore in a reverse polarity scenario you would have RCD protection but no overcurrent protection.

Both 1p+n and 2p will open both conductors when switched.
1p+n will sense overcurrent in the line, but not neutral.
2p will sense both.
Better to sense both when reverse polarity is a possibility, which is the case in EHU.

 

[roadtripper]

1p+n will sense overcurrent in the line, but not neutral.
2p will sense both.
Better to sense both when reverse polarity is a possibility, which is the case in EHU

There is no scenario where sensing over current in both lines, where one of them is Neutral and there is an RCD would behave any differently. If there is a current difference of more than 30ma the RCD element will trip both contacts.

You'd have to have a scenario where the fault current that could flow in the Neutral was sufficiently large that it could cause damage in the reaction time of the RCD, and you are not going to get that in single phase circa 16A EHU situations.

However using a 1P+N single RCBO is actually safer than the traditional RCD+MCB - because in over current the traditional MCB will only break the Line so in a reverse wired situation the Neutral would not be broken and remain live even though the MCB was "off". In the traditional design both lines are are only broken if the RCD trips.

The important thing is to ensure whatever you do that you have both lines broken by the RCD and you have a way of isolating both lines. Using just MCBs in an effort to save space would be dangerous.