MCBs Polarity ?

[Mikegh]

Quick question

Am I right in thinking that all standard SP MCBs are non -polarized

ie: supply can enter top or bottom of unless they're marked with line/load markings

Also the 1 and 2 markings on MCBs ,what does that indicate ?

 

[Mikegh]

I'm more familiar with the 1/2 3/4 5/6 on contactors and they have no polarity afaik

Are the numbers just to indicate the poles then ?

 

[Marvo]

It would come down to manufacturers instructions. Most are non polarized but I've come across some in the past that can't be connected in either direction.

 

[Mikegh]

Even if there's no polarity marked on the MCB ?

Would you still need to confirm it then ?

 

[Marvo]

Yeah, you should confirm it really. Usually with an MCB used on a pure AC circuit it doesn't matter but if theres a DC element to the supply or if it's used on a pure DC circuit then polarity can be important for efficient internal arc extinguishing.

See here for example Can we reverse the polarity of connections in C60H-DC MCB. | Schneider Electric India - https://www.se.com/in/en/faqs/FA374147/

 

[PEG]

I would be guided by the MI,as above. If they do not specifically approve fitment in either direction,then there is the answer.

A visual inspection of MCB's and a standard polarity check,would therefore confirm correct use.

Most modern collective board devices,are profiled to prevent reversal,due to clearance and cover aperture fitment.

Lots of things may look like they will work ok,when turned 180 degrees,but snakes,knives and girlfriends are not on that list ?

 

[brianmoooore]

For 'normal' AC applications a standard MCB is not polarity or direction sensitive, although the terminal clamp design may be designed for a busbar at one end and wires at the other.
1 and 2 markings? Some years ago, instant tripping (magnetic) curves of MCBs were indicated by types 1, 2 and 3. This has been replaced by letters (e.g B16, for a type B 16A MCB)

 

[Strima]

When Nader MCBs first emerged they were marked 'supply' and 'load', but the busbar fed them from the top in some applications, after several months we finally got a Chinglish answer from the manufacturers that it didn't matter in AC applications....

Not that it mattered anyway as they were using 100 amp MCBs a telecoms cabinet supplied from a 63 amp circuit so about as much use as a chocolate fireguard. Although they did come in handy as an isolator as they were double pole. The Chinese tend to rely on load limiting the equipment to protect the cable unlike our fangled western way of protecting the circuit...

 

[Lucien Nunes]

Important here is how you are defining polarity.

For a single-pole device in an AC circuit, the only applicable meaning is which side is the supply and which is load, and hence whch of the terminals remains live and which is isolated when the contacts are open. On a bare MCB this might not be significant but in an assembly e.g. with terminals and busbars there might be a preference or requirement to connect the supply to the side with better protection against accidental direct contact.. When the contacts are closed, the device has no sense of what orientation it is being used in, because the current is alternating.

For a DP or SPSN device two parameters are involved, supply / load and line / neutral. Obviously SPSN only has a tripping element in the line, so although again supply / load probably makes no difference, L/ N polarity is crucial. In a DP device specifically intended for SPN service the contact closure sequence might be defined with neutral closing first and opening last, so there might still be a difference between line and neutral poles.

On DC the situation is different, because the direction of current flow has a direct influence on the behaviour of the device, and MI's will tell if that is important.

This reminds me that one of the things I definitely want to make a video about when I eventually have time for that. is about the different meanings of polarity in different situations that are often not clearly distinguished. The main ones are:
Negative / Positive; which of two terminals in a circuit has the greater potential to give out electrons.
Anode / Cathode; which terminal is actually giving out electrons.
Neutral / Line; which terminal is held at earth potential.

 

[Mikegh]

When Nader MCBs first emerged they were marked 'supply' and 'load', but the busbar fed them from the top in some applications, after several months we finally got a Chinglish answer from the manufacturers that it didn't matter in AC applications....

Not that it mattered anyway as they were using 100 amp MCBs a telecoms cabinet supplied from a 63 amp circuit so about as much use as a chocolate fireguard. Although they did come in handy as an isolator as they were double pole. The Chinese tend to rely on load limiting the equipment to protect the cable unlike our fangled western way of protecting the circuit...

Load limiting is dol

Important here is how you are defining polarity.

For a single-pole device in an AC circuit, the only applicable meaning is which side is the supply and which is load, and hence whch of the terminals remains live and which is isolated when the contacts are open. On a bare MCB this might not be significant but in an assembly e.g. with terminals and busbars there might be a preference or requirement to connect the supply to the side with better protection against accidental direct contact.. When the contacts are closed, the device has no sense of what orientation it is being used in, because the current is alternating.

For a DP or SPSN device two parameters are involved, supply / load and line / neutral. Obviously SPSN only has a tripping element in the line, so although again supply / load probably makes no difference, L/ N polarity is crucial. In a DP device specifically intended for SPN service the contact closure sequence might be defined with neutral closing first and opening last, so there might still be a difference between line and neutral poles.

On DC the situation is different, because the direction of current flow has a direct influence on the behaviour of the device, and MI's will tell if that is important.

This reminds me that one of the things I definitely want to make a video about when I eventually have time for that. is about the different meanings of polarity in different situations that are often not clearly distinguished. The main ones are:
Negative / Positive; which of two terminals in a circuit has the greater potential to give out electrons.
Anode / Cathode; which terminal is actually giving out electrons.
Neutral / Line; which terminal is held at earth potential.

Polarity here

Supply in top or bottom