How do you choose the Rccb Rated Current

[yigitsdr]

Hi everyone,

How do you choose Rccb Rated Current at the your country?

Do you have an official document about it?

What do you reference for nominal current coordination with mcb before it?

How to calculate the rcd rated current and mcb rated current coordination, is there a document about it?

Thank you from now.

 

[SparkyChick]

If you are talking about the current carrying capacity of the device, yes it would be coordinated to be capable of handling the expected load current.

If you are talking about the tripping current, we typically use 30mA for additional protection (i.e. protection of the end user of the installation) and the protection of sockets rated at 32A or less, 100mA for sockets rated at >32A and for providing selectivity in some cases such as protection the internals of metal consumer units when the earthing system is TT and not exceeding 300mA for protection against fire.

I'm sure someone will correct me if I'm wrong

 

[yigitsdr]

If you are talking about the current carrying capacity of the device, yes it would be coordinated to be capable of handling the expected load current.

If you are talking about the tripping current, we typically use 30mA for additional protection (i.e. protection of the end user of the installation) and the protection of sockets rated at 32A or less, 100mA for sockets rated at >32A and for providing selectivity in some cases such as protection the internals of metal consumer units when the earthing system is TT and not exceeding 300mA for protection against fire.

I'm sure someone will correct me if I'm wrong

I know it, thanks, but Is there a formal calculation or figure that I can refer to for selecting the rated current, more about the selection of rated current that I want to learn?

 

[SparkyChick]

The RCCBs rated current carrying capacity should simply be large enough to handle the expected load. How you calculate that will depend on what it's supplying.

In domestic, the regulations suggest that RCDs should have upfront over current protection, so in a lot of our consumer units that means if the main service fuse is rated at 60A, the RCDs should be rated at 63A, if it's an 80A fuse, the RCDs should be able to handle 80A. Some suppliers such as Hager provide RCDs rated at 100A since this is the largest standard service fuse size in domestic installations.

Previously we would size the RCD for the expected load it was going to handle using diversity. You can find out about diversity and how it applies to sizing protective devices by doing a search on YouTube for SparkyNinja and Diversity. He's done a webinar recently about it and uploaded it to YouTube.

 

[telectrix]

If you are talking about the current carrying capacity of the device, yes it would be coordinated to be capable of handling the expected load current.

If you are talking about the tripping current, we typically use 30mA for additional protection (i.e. protection of the end user of the installation) and the protection of sockets rated at 32A or less, 100mA for sockets rated at >32A and for providing selectivity in some cases such as protection the internals of metal consumer units when the earthing system is TT and not exceeding 300mA for protection against fire.

I'm sure someone will correct me if I'm wrong

i wouldn't dare.

 

[yigitsdr]

So you say that the rcd rated current must be selected above the mcb rated current, do i understand right?

 

[SparkyChick]

Yes... if the MCB has a tripping current of 32A, then if the RCD is after it, it should have a current carrying capacity of at least 32A so that it isn't subjected to a protracted overload.

 

[yigitsdr]

For example, for a small house, how many ampere rcd do you choose after a mcb of 40A in the main breaker position?

 

[Andy78]

For example, for a small house, how many ampere rcd do you choose after a mcb of 40A in the main breaker position?

We don't put MCBs in the main breaker position, we generally use a double pole switch in domestic installations.

 

[telectrix]

generally the RCD comes before the breaker/s. in a lot of cases, the RCD serves several breakers, so it's current rating needs to be > the total of the breakers it feeds, allowing for diversity of the circuits. so if it feeds 4 x 32A breakers, but with a design load of all 4 being ,say, 75A. you would select a 80A or 100A RCD.
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where have all the avatars gone? mine, sparkchick,s and andy78 are all blank?????

 

[yigitsdr]

So how many amps do you usually use in the main circuit breaker position? How many amps do you choose RCD in such a house?
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Which network system are you using?
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If possible, can you share a sample fuse box image, to better understand amperage?

 

[telectrix]

im most houses here, each has a 80A or 100A supply with corresponding main supplier's fuse. the average house will have either a dual RCD dis. board, i.e. a 100A main switch with 2 RCDs, each either 80A or 63A, serving 4-6 circuits each... or each circuit protected by it's own RCDO (RCD and MCB combined.

dual RCD Board:

British General Fortress 12-Module 6-Way Populated Dual RCD Consumer Unit

Order online at Screwfix.com. Fully populated, 6-way dual RCD, insulated metal consumer unit. Flexible busbar. FREE next day delivery available, free collection in 5 minutes.

www.screwfix.com

 

[yigitsdr]

Thank you all for the answers, see you.

Best regards.