Electrical4less
electrical4less.co.uk › home › circuit protection advice › ⚡ what size rcbo do i need?
How To Choose The Correct RCBO | Complete Guide
April 9, 2026 - When people ask what size RCBO do I need, the correct answer depends on three core elements: ... Use Appendix 4 of BS 7671 to confirm that the cable used (e.g., 6mm², 10mm²) is capable of carrying that current based on how it’s installed.
Call: 020 7736 5755
Address: 9 Seagrave Road, SW6 1RP
Whirlpool
forums.whirlpool.net.au › home › air con › split system - new circuit?
Split System - New Circuit? - Air conditioners
Breaker size should be what is recommended in the AC manual. Cable size should be as per the Australian Standards (AS 3000 and AS 3008). Typically, 2.5mm2 cable is used for 16-20A circuits, while 4mm2 cable is used for 20-25A circuits.
RCD size selection
Nowadays really any new install domestically should be fully RCBOs. Almost every circuit in domestics needs RCD protection and I’m sure BS7671 states one circuit should not affect another. More on reddit.com
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April 11, 2024New build - Correct RCBO for aircon?
Electrician here. The Breaker is there to protect the cable, not your AC. Same with all the other breakers, the current capacity is matched with the cable, not with the end appliance. For the AC, I'd say your electrician has installed 6mm2. Depending on the route and distance the cable will be derated to accept a certain amperage, and there are calculators that can do this maths for you, I like jcalc. https://www.jcalc.net/cable-sizing-calculator-as3008 If he installed 6mm2, 2c+E, 20m, through your roof - partially surrounded by thermal insulation. Then 6mm2 is capable of 35A - not 40A. If you upsized the breaker to a 40A, then in 10 years time when the AC starts to shit the bed and the cable is humming with 38 amps and burns the house down you've got a problem. That said the 32A will be more than adequate. In normal operation if you tong test the AC it'll probably draw 10A max. If he installed 10mm2 it would have cost you a lot more, and wouldn't have been necessary. The sparky did the right thing and saved you money. Also if you had any device in your house drawing 32A regularly I'd hate to see your bill. In summary, it fine. More on reddit.com
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April 10, 2025Can replace 20a breaker with 25a???
Be better off calling an electrician and figure out the problem. Rather than upping the breaker, major hazard to life and safety. More on reddit.com
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September 22, 20213Ph vs 1Ph Aircon Energy Efficiency
There will be no difference in efficiency, or nothing of any significance. They all run through inverters anyway. 3ph unit might help with your phase balancing More on reddit.com
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April 1, 2024❓ Can I replace an MCB with an RCBO?
Yes — as long as there's enough neutral space and the circuit requires RCD protection (which it usually does). Always verify compatibility with your consumer unit.
electrical4less.co.uk
electrical4less.co.uk › home › circuit protection advice › ⚡ what size rcbo do i need?
How To Choose The Correct RCBO | Complete Guide
❓ Can I use a 40A RCBO for my EV charger?
Some EVs (up to 7.2kW) can use 32A RCBOs. Higher-demand chargers (11kW+) may require 40A — confirm with charger specs and cable route.
electrical4less.co.uk
electrical4less.co.uk › home › circuit protection advice › ⚡ what size rcbo do i need?
How To Choose The Correct RCBO | Complete Guide
❓ What size RCBO do I need for a cooker?
It depends on the load: under 2.9kW may be fine on a 13A plug, 3–7kW typically needs a 32A RCBO, and anything over 7kW often requires 40A or more.
⚠️ Always confirm with proper circuit design and cable sizing.
⚠️ Always confirm with proper circuit design and cable sizing.
electrical4less.co.uk
electrical4less.co.uk › home › circuit protection advice › ⚡ what size rcbo do i need?
How To Choose The Correct RCBO | Complete Guide
IET EngX
engx.theiet.org › f › wiring-and-regulations › 29172 › sizing-of-rcbo
Sizing of RCBO - Wiring and the Regulations BS 7671 - IET EngX - IET EngX
October 18, 2022 - The sizing of the overcurrent part of the RCBO protects the cables, not the loads.
Unicat
unicat.msf.org › cat › product › 43766
BREAKER RCCB AC, 30mA rated 25A, 2P inst.mod - Unicat
RCCB AC-type, 25A 30mA, 2P - (like poor insolation in underground cabling) but do NOT protect people.300/500 mA sensitivity RCDs provides a good protection against fire risk due to insulation failure between live conductor and earth. ... Do not connect one RCD/RCCB with more than 5 MCB's to prevent the so-called nuisance tripping. The RCD bloc must be ordered with its MCB or at least have an MCB of the same brand in order to install it in the proper way (this is a way to make an RCBO).
Price: €1.00
Unicat
unicat.msf.org › cat › product › 49051
RCCB A-type (A9R04225) 25A 300mA, 2P - Unicat - MSF
RCCB A-type (A9R04225) 25A 300mA, 2P - (like poor insolation in underground cabling) but do NOT protect people.300/500 mA sensitivity RCDs provides a good protection against fire risk due to insulation failure between live conductor and earth. ... Do not connect one RCD/RCCB with more than 5 MCB's to prevent the so-called nuisance tripping. The RCD bloc must be ordered with its MCB or at least have an MCB of the same brand in order to install it in the proper way (this is a way to make an RCBO).
Price: €1.00
Unicat
unicat.msf.org › cat › product › 49199
RCCB A-type, 25A 30mA, 2P | Unicat
RCCB A-type, 25A 30mA, 2P - (like poor insolation in underground cabling) but do NOT protect people.300/500 mA sensitivity RCDs provides a good protection against fire risk due to insulation failure between live conductor and earth. ... Do not connect one RCD/RCCB with more than 5 MCB's to prevent the so-called nuisance tripping. The RCD bloc must be ordered with its MCB or at least have an MCB of the same brand in order to install it in the proper way (this is a way to make an RCBO).
Price: €1.00
Unicat
unicat.msf.org › cat › product › 43765
RCCB AC-type, 25A 500mA, 4P | Unicat
RCCB AC-type, 25A 500mA, 4P - (like poor insolation in underground cabling) but do NOT protect people.300/500 mA sensitivity RCDs provides a good protection against fire risk due to insulation failure between live conductor and earth. ... Do not connect one RCD/RCCB with more than 5 MCB's to prevent the so-called nuisance tripping. The RCD bloc must be ordered with its MCB or at least have an MCB of the same brand in order to install it in the proper way (this is a way to make an RCBO).
Price: €1.00
Reddit
reddit.com › r/ukelectricians › rcd size selection
r/ukelectricians on Reddit: RCD size selection
April 11, 2024 -
I'm a bit confused when I'm studying about how to determine what size of RCD should be used. Here are some questions I'm struggling.
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One RCD with multiple MCBs? e.g. lets say 1x100A 30mA RCD with 10-20+ B6 MCB (extremely). theoretically is it valid? But in practice do I need to separate them? I generally can see the pattern 1xRCD with 4xMCB, unless total amp in 4xMCBs is larger than that RCD?
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How can I know what size of RCD should be used when doing design? Calculating the allowance of diversity refered Appendix A (On-site guide) to get approx. total number of amp, and get the closer RCB? e.g. if 4xMCBs = 62amp, i should get 63A RCD rather than 80A RCD?
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If no.2 is correct, I just found it is not easy to calculate total number of amp with diversity because i need to estimate the demand by researching appliance's power. Any quick ways can determine the size of RCD?
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Sometimes, I try to calculate the demand and find out the 100A supply may not enough for the demand? Let's say for example, 100A main supply may not enough for 6bedrooms 4 bathrooms 2kitchens house if it is in full load?
Sorry abit too long but thank you for the help.
Top answer 1 of 5
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Nowadays really any new install domestically should be fully RCBOs. Almost every circuit in domestics needs RCD protection and I’m sure BS7671 states one circuit should not affect another.
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Essentially, ignore load side. The current rating is the maximum the RCD can take - if it’s > the upstream OCPD, Then you’re all good.
Unicat
unicat.msf.org › cat › product › 43852
RCBO AC-type, C25 30mA 10kA, 1P+N - Unicat - MSF
RCBO AC-type, C25 30mA 10kA, 1P+N - (like poor insolation in underground cabling) but do NOT protect people.300/500 mA sensitivity RCDs provides a good protection against fire risk due to insulation failure between live conductor and earth. ... Do not connect one RCD/RCCB with more than 5 MCB's to prevent the so-called nuisance tripping. The RCD bloc must be ordered with its MCB or at least have an MCB of the same brand in order to install it in the proper way (this is a way to make an RCBO).
Price: €1.00
RS Components
nz.rs-online.com › web › content › discovery › ideas-and-advice › rcbo-guide
A Guide to RCBOs (Residual Current Circuit Breakers)
August 29, 2023 - For industrial or fire protection, you should ensure that the RCBO offers at least 10mA protection, has a 25A current rating, is SRIM certified, and provides A-type protection. Current rating: Choose a current rating (e.g., 16A, 20A, 32A) that ...
Clipsal
clipsal.com › home › products › circuit protection › max9
MAX9 Residual Current Breaker with Overcurrent Protection (RCBO) 1PN, 25A, 30mA, C Curve, 6000A, A Type, SLIM
MAX9 Residual Current Breaker with Overcurrent Protection (RCBO) 1PN, 25A, 30mA, C Curve, 6000A, A Type, SLIM - View the MX9R3125 product features, specifications, documents and FAQs. MAX9 Residual Current Breaker with Overcurrent Protection (RCBO) 1PN, 25A, 30mA, C Curve, 6000A, A Type, SLIM.
Price: A$108.00
Sparky Direct
sparkydirect.com.au › home › electrical › circuit protection › rcbo › single pole rcbo › clipsal single pole rcbo
Clipsal 25AMP RCBE225/30S RCD/MCB 1P+N 1M 25A 4.5kA 30MA SLIM RCBO
Clipsal RCBE225/30S | 25AMP RCBO 1P+N 4.5kA Resi MAX - Clipsal by Schneider Electric | RCBO 25A 1P+N 4.5kA Resi MAX | C Curve, 30mA Type A The Clipsal RCBE225/30S is a single-module RCBO rated 25A with 30mA earth-leakage protection, combining overcurrent and residual-current protection in one device. Part of
Price: A$35.72
Wosomelec
wosomelec.com › blog › rcbo-ultimate-guide
RCBO Ultimate Guide(Residual Current Circuit Breakers) - LAIWO Electrical Technology
September 27, 2025 - Before proceeding with the installation, you should ensure that the RCBO offers at least 10mA protection, has a 25A current rating, is SRIM certified, and provides A-type protection. You will also require ready access to both live and neutral wiring...
Elec-Mate
elec-mate.com › home › electrical guides › rcbo installation guide
How to Wire an RCBO: 4 Steps + Neutral Rule | Elec-Mate
June 10, 2026 - Type F RCBOs additionally detect higher-frequency currents and are suited to circuits supplying variable speed drives and modern inverter equipment. 04BS 7671 Section 531.3 covers the requirements for residual current devices. Regulation 531.3.3 determines the correct device type (AC, A, F or B) from the DC components and frequencies a load can produce, and Regulation 531.3.2(b) recognises RCBOs on individual final circuits in residential premises as a way to limit unwanted tripping.
Screwfix Community Forum
community.screwfix.com › forums › screwfix community forum › electricians' talk
Requirement for RCBs on each circuit of a consumer unit | Screwfix Community Forum
July 24, 2020 - It is a problem knowing if a RCD is OK for a circuit at the design stage, with AC current there are always some losses, so it is considered 9 mA is the limit for a single 30 mA RCD, but although once built easy enough to put a clamp on ammeter around the cables, by this time it is too late, with a hi integrity CU you can have a couple of circuits on their own RCD (RCBO) but size of the premises does matter.
Reddit
reddit.com › r/auselectricians › new build - correct rcbo for aircon?
r/AusElectricians on Reddit: New build - Correct RCBO for aircon?
April 10, 2025 - You'll need 10mm2 to get 40A. Also, for the people that have already commented otherwise, there's a clause in the new standards that you must abide by manufacturer instrucions/specifications.
Westhomes
westhomesele.com › blogs › how-to-choose-the-right-rcbo-for-your-electrical-panel
How to Choose the Right RCBO for Your Electrical Panel
July 3, 2026 - Q4 Why does RCBO trip frequently? It may be caused by leakage current accumulation or improper load selection. Q5 How do I choose breaking capacity? It must be higher than the system’s maximum short-circuit current.
Screwfix Community Forum
community.screwfix.com › forums › screwfix community forum › electricians' talk
RCD size choice | Screwfix Community Forum
July 19, 2020 - Type A can cope with d.c. leakage up to 6mA. Type F up to 10mA. Type B however are not affected by d.c. leakage. (Type B are recommended for use with solar panels and Electric car chargers.) All manufacturers produce type AC RCBOs (which are actually banned in many countries).