Socket Breaker

[spark 68]

MCBs whith higher instantaneous trip current values are used, where high start up currents are expected.
For example where there are DOL motors, lots of fluorescent lights, electric heaters, etc.

Yes I know Spin, the OP he asked about selection for general use S/O, I am aware he is from the US, but as far as I can gather he is certifying a product for Europe/UK, a type B gives a reasonable compromise for max Zs V inrush requirements, unless he has something specific in mind which may need a higher rated type.

 

[D Skelton]

Id imagine a L-N fault would be less of a hazard to humans in terms of shock, but it sounds like the regs want identical tripping for both L+PE and L+N.

No, there is no maximum permitted disconnection time for L-N faults.

 

[spark 68]

No, there is no maximum permitted disconnection time for L-N faults.

As the E connection is usually derived by way of the starpoint N, it is generally given that if an OCPD will comply L-E, then it will also comply L-N.

 

[D Skelton]

As the E connection is usually derived by way of the starpoint N, it is generally given that if an OCPD will comply L-E, then it will also comply L-N.

The two types of fault have different consequences. The very nature of a L-N fault means that there is no need to put a maximum permitted disconnection time to it. Instead, protection is afforded by ensuring that the cable can carry a given prospective short circuit current without causing damage to it for the time it takes for disconnection to occur. There is no given time for disconnection to comply with during a L-N fault.

 

[spark 68]

The two types of fault have different consequences. The very nature of a L-N fault means that there is no need to put a maximum permitted disconnection time to it. Instead, protection is afforded by ensuring that the cable can carry a given prospective short circuit current without causing damage to it for the time it takes for disconnection to occur. There is no given time for disconnection to comply with during a L-N fault.

Both are actually quite sweeping and broad statements

For instance a look at table 7.1 in the OSG for max circuit length and allowed installation methods, where only OCPD (no RCD) is present then Zs is the limiting factor first, when an RCD is thrown into the mix then SC becomes the limiting factor.

As always there are exceptions to every rule

 

[D Skelton]

Both are actually quite sweeping and broad statements

For instance a look at table 7.1 in the OSG for max circuit length and allowed installation methods, where only OCPD (no RCD) is present then Zs is the limiting factor first, when an RCD is thrown into the mix then SC becomes the limiting factor.

As always there are exceptions to every rule

Of course, but one hard and fast rule is that unlike L-E faults, L-N faults have no max disconnection time, which was the misconception I pointed out. That statement is of course made with limiting factors disregarded.

 

[Gardner]

For general use sockets Type B is normally used, the instantaneous trip part is 5X In, these will be adequate for normal loads unless you have something specific in mind that may need a breaker requiring a higher threshold.

Yes, thank You! That was my biggest concern.

 

[Gardner]

The two types of fault have different consequences. The very nature of a L-N fault means that there is no need to put a maximum permitted disconnection time to it. Instead, protection is afforded by ensuring that the cable can carry a given prospective short circuit current without causing damage to it for the time it takes for disconnection to occur. There is no given time for disconnection to comply with during a L-N fault.

Thats what I was thinking. A L+N fault would not cause a voltsge rise to remote eartt while the fault is happening. I could see LN faults being the same as LPE faults in TN-C-S, but earth loop impedance would be different with a smaller PE like 1.5mm PE with 2.5mm LN or a TN-S network?

 

[spark 68]

Do you have access to BS7671 Gardner ?

If you do then have a look at appendix 15

 

[Gardner]

Both are actually quite sweeping and broad statements

For instance a look at table 7.1 in the OSG for max circuit length and allowed installation methods, where only OCPD (no RCD) is present then Zs is the limiting factor first, when an RCD is thrown into the mix then SC becomes the limiting factor.

As always there are exceptions to every rule

Can you rxplain further? This is exsctly what I eas thinking of, in that RCD automatically fulfills disconnect under all typical circuit impedances such as very long runs? Sorry for the triple post im on my phone lol

 

[Gardner]

Do you have access to BS7871 Gardner ?

If you do then have a look at appendix 15

I do, fortunately

 

[spark 68]

It might help us a bit better to help you, if you explain what exactly you are trying to achieve and exactly what you want to know.

 

[Gardner]

It might help us a bit better to help you, if you explain what exactly you are trying to achieve and exactly what you want to know.

Basically how to meet disconnect times and earth fault loop impedance. If the breaker is over sized relative to the short circuit current trip times can be exceeded.

 

[spark 68]

Basically how to meet disconnect times and earth fault loop impedance. If the breaker is over sized relative to the short circuit current trip times can be exceeded.

Some of this we cannot predict without a lot more information, the Ze (external Earth loop impedance) is beyond our control so more information is needed here, what type of cabling is used, how it is installed and length of circuit all has a bearing on current carrying capacity, R1+R2, etc...etc.., how are we supposed to help you with no information given ?
This is like asking how long is a piece of string ?

 

[Deleted member 26818]

Don't really think that any extra information is required.
The OP is really just asking what type of MCB should be used for general circuits.
Unfortunately, they've gone about asking the question in a rather round about fashion.
The answer of course being Type B.