Which size rcd

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You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser. Ray Pooley -. Reaction score I have had a good search for this information but can't find it anywhere not even in my on site guide 17th edition. You decide you want to install an RCD. You do your max load and diversity calculations for each MCB circuit and you come out with 10 current values that will invariably be less than the rating of the MCBs.

Do you add up the max demand and diversity currents? The current ratings of the MCBs? Or is there a formula similar to the max demand and diversity rules for MCBs that you deploy to the RCD size calculation? Is this calculation something that can lead to a decision to split the CU if a single RCD can't cover the entire unit?

Reaction score 65, Click to expand SparkyChick Mod. Reaction score 7, Toggle navigation. Search Topic. Topic Tools. View similar topics Print this topic. If we take a amp fuse feeding a amp switch which feeds 10 MCB's totalling amp I can see the reasoning behind this in that it is unlikely that enough items will be used at the same time to overload the A switch and even if they do the worse case scenario is to blow the amp fuse. Yet it is the way Wylex bundle the boards as sold by Screwfix.

Had they not been sold in this way I would have failed the installation as Code 2. I don't know why a unit of the same physical size should have ratings of 63 amp, 80 amp and amp but I note the price increases and would have assumed you should not allow over 63 amp to pass through that version.

I would be interested to hear what others think about this. All best Eric Palmer. Top : Bottom. I have a RCD instruction leaflet somewhere Wylex I think ,that states they need backing up by 60, 80 or amp fuses respectively, yet that is not how they are installed. That means the manufacturers agree with you! I will have a look after the Holiday weekend and see if I can find it Tenby again in the morning!

Andy Betteridge. Originally posted by: ericmark I don't know why a unit of the same physical size should have ratings of 63 amp, 80 amp and amp but I note the price increases and would have assumed you should not allow over 63 amp to pass through that version.

They are actually RCCB's which means the reccomended maximum switching capacity of the contacts is 63A. I was explaining this to my apprentice If you imagine a fairground turning up and wanting a huge suppy switching on to a temporary site, they traditionally use big linked throw-over switches, because of the possibility of their being hundreds of amps load when they switch them on - THEIR BIG BOYS!!

That therefore is the rating of the contacts, say Amps. The minimum rating of circuit breaker should be 8A. The recommended size of circuit breaker should be. To find the breaker size for three phase supply voltage, we must know the exact kind of load as there are many factors affecting the load current. Good to know: For the same load, the breaker size in three phase is less than the breaker size used in single phase AC circuits. Lets find the correct size of circuit breaker for three phase circuits as follow.

Example 1: Which size circuit breaker is needed for 6. The recommended size of circuit breaker is. The next closest standard of circuit breaker is 10A. Recommended Size of Circuit Breaker: 1. The next closest value is 30A. This is because all loads are not same i.

This way, a 30A circuit can be safely used for 24A circuit. In other words, a load circuit having 24A, the appropriate size of breaker would be:. In addition, A Circuit breaker rated for:. Keep in mind that the breaker size should not increase the max amperage rating of cable and wire. The following two charts shows the suitable circuit breaker sizes with wire gauge and different level of voltages.

RCDs detect fault currents leaking to earth either through metalwork or unfortunately in some cases through a person's or animal's body. Because of the way in which they work they can detect very small currents which cannot be achieved by any other device and provide the only practical method of protecting against the effects of these small currents. Effects of Electric Shock If a person comes into contact with metal which is carrying electric current and at the same time is earthed either through the other hand or the feet, a current will flow through the body dependant on the resistance of the body and the voltage of the supply.

At volts this current could vary between thousandths of an amp. Solutions Firstly to have a low enough voltage that a dangerous current could not flow though the body. This would be 50 volts or below. Although this is used in special cases it is not practical for normal domestic or commercial premises. Secondly to prevent people coming into contact with dangerous voltages. This is the object of barriers and enclosures. As we know from experience these are not foolproof.

The third and only practical way on mains voltage is the RCD which will detect that a fault current is leaking to earth and then cut off the supply rapidly enough to prevent dangerous effects. You will recall earlier that the level of current which flows through the body in the event of a shock situation is between 80 mA and mA.