type D m.c.b's in hotel/resturaunt

[Tosh]

Hi ppl ,some advice needed. does any one know what pir code it would be for having type d m.c.b's on just normal socket and lighting circuits?. to my understanding these should be changed,

 

[Deleted member 9648]

As long as the required disconnection times are met on the circuits concerned no code.
Measure the Zs at the furthest point on the circuit and as long as the max Zs for the type D mcb is greater than your measured Zs no problem....also keep in mind that if the circuits are 30ma RCD protected the required disconnection time will be met with a Zs of up to 1667 ohms.
This has come up before and the only consideration as far as the regs and PIR's are concerned is the disconnection time...whether the device is a type B/C/D mcb...semi-enclosed fuse....whatever,if i'ts listed as a protective device in the BRB and it meets the disconnection time it complies.

 

[Tosh]

As long as the required disconnection times are met on the circuits concerned no code.
Measure the Zs at the furthest point on the circuit and as long as the max Zs for the type D mcb is greater than your measured Zs no problem....also keep in mind that if the circuits are 30ma RCD protected the required disconnection time will be met with a Zs of up to 1667 ohms.
This has come up before and the only consideration as far as the regs and PIR's are concerned is the disconnection time...whether the device is a type B/C/D mcb...semi-enclosed fuse....whatever,if i'ts listed as a protective device in the BRB and it meets the disconnection time it complies.

I see what you mean, but how does this work with a 10% test when most breaker are type D.that will be fine for the circuits tested, its just when i did my 17th the niceic guy said he had a problem with a site once where the spark used type D m.c.b's on a full domestic site and he pulled him up for it as a non compliance as there meant to be used for industrial use etc,. just don't want to pass a job if this can come back to haunt me...

 

[Deleted member 9648]

They are intended for high inrush current applications, but I cannot see how it can be a non compliance if the disconnection times are met......................be interested in other peoples views thoiugh.
Regarding the 10% test I assume you mean 10% of the installation is checked.....it seems to me that regardless of the type of protective device it will be necessary to confirm disconnection times are met .....whether a fuse,type B mcb,type d mcb...whatever.Just because i'ts say a type b you cannot assume it will comply any more than you can assume a type d wont.

 

[Tosh]

They are intended for high inrush current applications, but I cannot see how it can be a non compliance if the disconnection times are met......................be interested in other peoples views thoiugh.
Regarding the 10% test I assume you mean 10% of the installation is checked.....it seem to me that regardless of the type of protective device it will be necessary to confirm disconnection times are met .....whether a fuse,type B mcb,type d mcb...whatever.Just because i'ts say a type b you cannot assume it will comply any more than you can assume a type d wont.

I was thinking the same about disconnection times as soon as i sent the reply, it's just the fact that the nic guy mentioned it and at the time he said is was because the wholesalers where selling them cheapl .i just don't c the point in it being fitted with type D breakers .thanks for the replies

 

[Risteard]

I was thinking the same about disconnection times as soon as i sent the reply, it's just the fact that the nic guy mentioned it and at the time he said is was because the wholesalers where selling them cheapl .i just don't c the point in it being fitted with type D breakers .thanks for the replies

Presumably he meant that they had been put in without understanding that there is a significantly lower Zs required. Not that they can't be used. Although a Type D would be highly unusual in a domestic environment.

 

[JUD]

As long as the required disconnection times are met on the circuits concerned no code.
Measure the Zs at the furthest point on the circuit and as long as the max Zs for the type D mcb is greater than your measured Zs no problem....also keep in mind that if the circuits are 30ma RCD protected the required disconnection time will be met with a Zs of up to 1667 ohms.
This has come up before and the only consideration as far as the regs and PIR's are concerned is the disconnection time...whether the device is a type B/C/D mcb...semi-enclosed fuse....whatever,if i'ts listed as a protective device in the BRB and it meets the disconnection time it complies.

Remember that an MCB also provides line-neutral short circuit protection. An RCD won't disconnect a L-N fault so R1 + Rn also needs to meet maximum Zs values.

Take a look at Table 7.1 in the OSG. Type D circuit breakers are not permitted on a lot of circuits for this very reason and if they are they are very short runs.

 

[Tosh]

Remember that an MCB also provides line-neutral short circuit protection. An RCD won't disconnect a L-N fault so R1 + Rn also needs to meet maximum Zs values.

Take a look at Table 7.1 in the OSG. Type D circuit breakers are not permitted on a lot of circuits for this very reason and if they are they are very short runs.

Thanks for the reply, just checked the on site guide there and c what you mean, theres gona be a lot that dont complie only problem is it was only a 10% test, so would i put a code 3 in for all circuits with a type d breaker? any advice would be helpfull.. thanks

 

[dichroic]

Although every comment regarding maximum ZS and required disconnection times for this topic are equally valid i must point out that there is more to this problem than meets the eye. Lets not forget what the D type breaker is going to allow to happen in an overload condition.


In the event of an overload, in the absence of a protective device, the temperature of the circuit conductors would rise excessively, possibly damaging the insulation, joints and terminations of the conductors, and /or their surroundings.

To protect against such damage, the design of the circuit has to properly co-ordinate the current-carrying capacity of the conductors and the anticipated load current with the characteristics of the overload protective device.


It is therefore essential that the design provides for the circuit and its surroundings to be protected from damage caused by the rise in the temperature of the circuit conductors due to overload current flowing in them.

Regulation 433.1 requires every circuit to be designed so that a small overload of long duration is unlikely to occur.
Such an overload can result where, due to inadequate design, the design current of the circuit (

) is too small for the load, such that the current in the circuit just exceeds both

and

. The small overload current, though probably insufficient to operate the protective device, is liable to raise the temperature of the circuit conductors to above the rated value. This situation must be avoided, as it can lead to premature ageing and deterioration of insulation and connections.


Regards

Dichroic

 

[Deleted member 9648]

Although every comment regarding maximum ZS and required disconnection times for this topic are equally valid i must point out that there is more to this problem than meets the eye. Lets not forget what the D type breaker is going to allow to happen in an overload condition.


In the event of an overload, in the absence of a protective device, the temperature of the circuit conductors would rise excessively, possibly damaging the insulation, joints and terminations of the conductors, and /or their surroundings.

To protect against such damage, the design of the circuit has to properly co-ordinate the current-carrying capacity of the conductors and the anticipated load current with the characteristics of the overload protective device.


It is therefore essential that the design provides for the circuit and its surroundings to be protected from damage caused by the rise in the temperature of the circuit conductors due to overload current flowing in them.

Regulation 433.1 requires every circuit to be designed so that a small overload of long duration is unlikely to occur.
Such an overload can result where, due to inadequate design, the design current of the circuit (

) is too small for the load, such that the current in the circuit just exceeds both

and

. The small overload current, though probably insufficient to operate the protective device, is liable to raise the temperature of the circuit conductors to above the rated value. This situation must be avoided, as it can lead to premature ageing and deterioration of insulation and connections.


Regards

Dichroic

Reg 433.1 states the requirements for co-ordination between protective device and conductor to prevent overload damage......reg 433.1.2 lists the protective devices which will meet the requirements of 433.1, which includes Bs 60898 mcb's of all types.

 

[dichroic]

Wirepuller,

You obviously didn't understand my post. Can you read it again !!

Have a look at regulation 433.1.1 (iii)

Regards

Dichroic

 

[Deleted member 9648]

I did read and understand your post....regardless of the type of protective device chosen conditions (i)and (ii) of reg 433.1.1 would have to be met....reg 433.1.2 states that condition (iii) of 433.1.1 will be met if one of the protective devices listed is chosen,which includes all type 60898 mcb's..