mccb as main switch

[0151]

guys I have a BS 60947-2 1200 amp "bticino" mccb as a main switch but trying to track down the company for a max Zs is a nightmare.

my question is if it is being used as a main switch on a panel does it still requie the max zs info??

they are part of legrand now and legrand technical will only deal with the door entry and lighting control stuff these guys make??

if i do need to put the Zs info in could i use say sqD info or is that not reccomended

 

[binky]

Not quite sure what you are getting at here - Zs is not dependent on the MCCB, unless you are getting a high resistance through it (ie it's faulty)?? Zs is dependent on DNO supply characteristics ie TN-s, TT etc and the meter tails etc, which is what you are checking when taking Zs readings. I hasten to add I mostly do domestic and this sounds like a 3 phase set up, so could be talking non-sense.

 

[sparkytim]

Why is the MCCB fitted?

If at the origin then Max Zs value not required as the supply Fuse provides adequate protection for the tails and your outgoing MCBs provide protection for each circuit

If it at the end of a Distribution circuit then the supply end protective device protects the circuit.

Or perhaps you mean PFC value for the device? this should be marked on it.

 

[0151]

thanks guys.

its a 1200 amp mccb on a large panel and as you pointed out each outgoing circuit is protected by smaller mccbs which i fortunatly have the max zs info for.

I decided to just put the RECs info down and treat it just as an isolator instead of trying to be a smart arse

thanks again

carl

 

[Lurch]

I'd still like to know what the question was?

 

[sparkytim]

my question is if it is being used as a main switch on a panel does it still requie the max zs info??

I think this was it

 

[Lurch]

my question is if it is being used as a main switch on a panel does it still requie the max zs info??I think this was it

That's why I was confused.

 

[batty]

For a 1200amp MCB it would need to be extremly low I think.

 

[binky]

thanks guys.its a 1200 amp mccb on a large panel and as you pointed out each outgoing circuit is protected by smaller mccbs which i fortunatly have the max zs info for.

thanks again

carl

Right so its just a main switch then and the individual circuits are 'fused down' accordingly. The 1200A thing is just its load capacity ie its big enough to carry total load for the system and still operate as a switch without melting - its the same as the 100A main switch in standard domestic CUs, you don't get a Zs based on the main switch, but on the individual circuits, you take Ze at the main switch. If the panel is a fed from another panel (ie by distribution circuit) then you need to check the feed panel for a suitable 'fuse' to protect the cable supplying your panel with the 1200A MCB. I hope that makes sense :^O

 

[netblindpaul]

Ah but, an mccb is an overload protective device.

I don't believe that anyone on here has instruments sufficiently accurate to measure the Zs at a 1200A mccb to the required levels!

You would need a 4 wire milli ohm meter or a ductor tester to get sufficiently accurate results!

Well...

As long as the upstream cpd will protect the circuits up to the input to the final circuit mcb's then perhaps you could ignore the issue.

I have done this in the past with an mccb, as long as the pfc is below the fault rating of the mccb though, most are 25 or 35kA.

UNLESS you have sufficient upstream protection.

Remembering that protection does not meen that the downstream devices are re-useable, just that no "collateral" damage is caused!

 

[binky]

Ah but, an mccb is an overload protective device.I don't believe that anyone on here has instruments sufficiently accurate to measure the Zs at a 1200A mccb to the required levels!

Sorry Paul, showing my ignorance of large 3 phase gear - seems strange to have an mccb protecting mccbs (thought it was a typo), hence would treat as main switch, but perhaps I should shut up before displaying any more ignorance :coat

 

[netblindpaul]

I took the board to be an MCCB incomer with MCB outgoers?

MCCB = Moulded Case Circuit Breaker.

MCB = Miniature Circuit Breaker.

Typical breaking capacity for MCB circa 10kA (max)

Braeking capacity for MCCB perhaps 35kA.

Little different! O)

If you are interested look on the Schneider group site and you can download some data giving examples of how to achieve discrimination between such devices.

Discrimination is a complex field and it can be total or partial depending on the CPD's.

Hence my query about Amtech software elsewhere.

Discrimination can be VERY important on large multi DB installs.

You don't want a lamp failure taking out half a production facility employing 100's of people because you got your discrimination assessment/studies wrong!

 

[Oracle]

Wait until you start playing with ACB's and current injectors

O.

 

[netblindpaul]

NAHHHHHH, I have ONE customer with an incoming ACB, that's enough!

The main switch / cb is 6m away from the 11kV sub.

You can feel & hear the lectrickery!