Quick question and little help

[Ruso]

Q-state 3 factors that influence selection of a protective device??

Would this be
1-cable size
2-ambient temp
3-equipment??

What you think? I've tried to answer best I can

 

[malcolmsanford]

Well nearly

1) Load
2) Type of load such as inrush currents therefore for a MCB type B,C,D
3) ADS

 

[Ruso]

Thanks for your reply. Could you explain 2 and 3 mate

 

[malcolmsanford]

2) Type of MCB/Fuse/RCBO is dependent of inrush currents. Simple example would be say a welding machine, because there are high currents (inrush currents) when the unit starts you would pick a D type breaker so that it would not trip, these loads are inductive loads. A immersion heater would only require a B type breaker as you would have none of these inrush currents and is call a resistive load. So you choice breaker will be dependent on type of load inductive or resistive

3) Depending on additional protection provided by an RCd. For instance circuits in a room containing a bath and shower have to be protected by 30mA RCD, so that influences your selection of protection devices, as it's a regulation, these regulations come under the Automatic Disconnection of Supply or ADS

 

[Ruso]

Fantastic that's for explanation m8

 

[SirKit Breaker]

Prospective fault current is another. Your chosen device must be capable of withstanding the higher of the prospective earth fault current, or prospective short circuit current of installation, if it doesn't then it could fail to operate in the required time, or not operate at all.

Cheers.........Howard

 

[Paul.M]

Q-state 3 factors that influence selection of a protective device?

I would say:-

1. The cable size and type of circuit. (6A, 10A,16A,20A etc)
2. Start up current. Type B, type C etc.
3. The maximum fault current it can handle without being replaced. eg 6KA, 10KA.


Ask yourselves this.... What three things are printed on an MCB?

 

[Jonny66]

Ib<In<Iz (and I2<1.45Iz)

1) Design current Ib
2) Nominal current of protective device In
3) Current carrying capacity of cable Iz

 

[vjsmarwick]

the circuit breaker is chosen to provide safety for the circuit so,
(1) Cable size and test results so that it trips / blows before your circuit is damaged.
(2) Type of load so that you can choose B,C,D or RCBO or any other variant but for old fashioned rewire-able or cartridge then that would not be a factor.
(3) Type of enclosure no point trying to jam an MCB in to a rewire-able board or a new Wylex MCB in to an old Wylex MCB board as it just wont fit.

 

[telectrix]

and a most important factor in selecting the correct protective device is..... can you get it in with a hammer...oops, sorry, thought i was on the plumbers forum. :drool5:

 

[dim_bulb]

There are a lot of other protective devices bs 88, 1362 etc so I doubt it's asking for the type. I would be going for design current, pfc, etc