RCD Ratings Explained – 40A, 63A, 80A, 100A & 30mA
When looking at an RCD, you'll usually see several different electrical ratings printed on the front.
Common examples include:
40A 30mA
63A 30mA
80A 30mA
100A 30mA
These numbers describe different characteristics of the RCD and shouldn't be confused with each other.
If you're trying to identify or replace an existing RCD, understanding these markings is important.
What Does 40A, 63A, 80A or 100A Mean on an RCD?
The rating shown in amps (A) is the RCD's rated current.
Common ratings found in UK consumer units include:
- 40A
- 63A
- 80A
- 100A
This rating relates to the current the RCD is designed to carry under its specified operating conditions.
It is completely separate from the residual-current rating.
For example:
80A 30mA
doesn't mean the RCD trips when the circuit reaches 80A.
The 80A and 30mA figures describe two different characteristics.
What Does 30mA Mean?
The 30mA marking refers to the RCD's rated residual operating current.
An RCD monitors the current flowing through the conductors passing through it.
If an imbalance occurs because current is flowing through an unintended path, the RCD can disconnect the supply when the relevant residual-current conditions are reached.
30mA RCD protection is extremely common in domestic installations where additional protection is required.
80A vs 30mA – What's the Difference?
A simple way of understanding the markings is:
80A = Rated current
30mA = Rated residual operating current
Therefore, an:
80A 30mA RCD
is an RCD with an 80A rated current and a 30mA rated residual operating current.
The two numbers shouldn't be compared directly because they describe different things.
Does a 100A RCD Provide More Protection Than an 80A RCD?
Not necessarily.
A higher rated current doesn't mean that the RCD provides a greater level of residual-current protection.
For example:
80A 30mA
and
100A 30mA
can both have the same 30mA rated residual operating current.
The difference is their rated current.
The appropriate rating needs to be selected according to the design and requirements of the installation.
Can I Replace a 63A RCD With an 80A RCD?
You shouldn't choose a replacement simply by selecting an RCD with a higher amp rating.
RCD selection depends on the design of the electrical installation and the equipment with which the device is being used.
When replacing an RCD, factors can include:
- Rated current
- Rated residual operating current
- RCD type
- Number of poles
- Manufacturer
- Consumer unit range
- Compatibility with the assembly
- Upstream protection
- Installation design
- Manufacturer's instructions
The replacement should therefore be selected based on the complete specification rather than assuming that a larger amp rating is automatically better.
Can I Replace an 80A RCD With a 100A RCD?
Again, not simply because both devices physically fit.
An electrician assessing the installation needs to establish whether the replacement device is suitable for the consumer unit and the electrical characteristics of the installation.
The manufacturer's compatibility information should also be followed.
What Does 30mA vs 100mA Mean?
Not every RCD has a 30mA residual-current rating.
Other ratings exist, including 100mA and 300mA, depending on the application and required protection.
These should not be treated as interchangeable.
For example, replacing a 30mA RCD with a 100mA RCD simply because the current rating and physical dimensions are similar would fundamentally change the residual-current protection provided.
The correct residual-current rating must be selected for the particular application.
RCD Rating vs MCB Rating
RCD and MCB ratings are also commonly confused.
An MCB marked:
B32
is a 32A circuit breaker with a Type B tripping characteristic.
An RCD marked:
80A 30mA
is describing its rated current and rated residual operating current.
Traditional split-load consumer units commonly use an RCD to provide residual-current protection to a group of circuits, while individual MCBs provide overcurrent protection for those circuits.
The RCD is therefore performing a different function from the individual MCBs.
RCD Rating vs RCBO Rating
An RCBO combines residual-current protection with overcurrent protection.
For example, an RCBO may be marked:
B32 30mA Type A
This provides overcurrent protection for an individual 32A circuit as well as residual-current protection.
An RCD marked:
80A 30mA Type A
doesn't perform the same function as an 80A circuit breaker.
The 80A figure is the RCD's rated current.
Does RCD Type Matter as Well as the Rating?
Yes.
Matching:
80A + 30mA
isn't enough to identify the correct replacement.
You also need to establish the RCD type.
Common examples include:
- Type AC
- Type A
There are also Type F and Type B devices for applications requiring those characteristics.
See our Type A vs Type AC RCD Guide for a more detailed explanation.
Does the Number of Poles Matter?
Yes.
RCDs are manufactured in different configurations depending on the electrical system and application.
Many domestic single-phase consumer units use two-pole RCDs, switching the relevant live and neutral conductors.
Other installations may require different configurations.
The replacement device needs to match the requirements of the installation.
How to Read an RCD Before Ordering a Replacement
Before purchasing an RCD, take a clear photograph of the front of the existing device.
Look for:
Manufacturer
For example Wylex, Hager or Crabtree.
Model number
This is often the most useful information for identifying the exact device.
Rated current
For example 63A, 80A or 100A.
Residual-current rating
Commonly 30mA in domestic applications.
RCD type
For example Type AC or Type A.
Number of poles
Check the configuration of the existing device.
Example
If your existing RCD says:
Wylex – 80A – 30mA – Type A
don't search only for:
“80A RCD”
Instead, identify the exact Wylex range and product number as well.
This significantly reduces the risk of ordering an incompatible device.
Can Different Brands of RCD Be Interchanged?
You should not assume so.
An RCD manufactured by Wylex shouldn't automatically be replaced with a Hager, Crabtree, Schneider or another manufacturer's device simply because the ratings appear identical.
Consumer units are assemblies, and the compatibility of the protective devices with that assembly matters.
Even products from different generations made by the same manufacturer may not necessarily be interchangeable.
Always identify the consumer unit range and exact RCD model when looking for a replacement.
Finding Older and Discontinued RCDs
Older consumer units can sometimes contain RCDs that are no longer part of the manufacturer's current product range.
This doesn't mean that searching only for a modern RCD with similar ratings will identify the correct replacement.
The original model number is particularly useful when searching for discontinued electrical equipment.
At ReCircuit Resale, we regularly stock current and discontinued RCDs from manufacturers including Wylex, Hager and Crabtree.
If you're struggling to identify an existing device, send us a clear photograph of the RCD, its model number and the consumer unit and we can help identify the equipment you're looking for.
This guide is intended for general product identification. The correct rating and type of RCD must be determined from the requirements of the electrical installation. Work within consumer units and fixed electrical installations should be carried out by a suitably competent person in accordance with BS 7671 and the manufacturer's instructions.