Chase down and reduce the earth leakage current? Would you consider this a вЂњfaultyвЂќ installation?ДЄny thoughts will be gratefully received, and IвЂ™ll be sure to let you know how it goes.Get the DNO to check the overhead cable before changing the consumer unit.Change the consumer unit to all-RCBOs вЂ“ this is expensive for the customer and I canвЂ™t give a 100% guarantee that the tripping will ceaseвЂ¦ how much earth leakage could a mains-borne transient or fault cause? It has the benefit that, if I have missed a circuit fault, it will be isolated by an RCBO when it next occurs.Change the consumer unit for a split load dual RCD configuration вЂ“ with careful assignment of the circuits each RCD will carry roughly 8.5mA of standing earth leakage, but will this give immunity to further tripping, maybe a three-way split required?.How should I proceed to be sure of resolving the problem, and in a cost-effective way? What is the maximum level of earth leakage acceptable in any given circuit for it to be considered safe? The 30% limit (9mA in this case) of 531.3.2? The random tripping, symptom (1), is being caused by supply side transients (or maybe even an intermittent fault in the overhead cable) and/or a high impedance neutral-to-earth fault somewhere in the installation. The fluorescent lights and tumble drier are likely to draw a transient earth leakage current >6mA when they start which explains symptom (2). The RCD is (quite severely) sensitised by the 17.0mA standing earth leakage current, it will trip when a further 6mA of leakage current is drawn. A repaired ring circuit in the kitchen draws 6mA of the earth leakage, a garage circuit draws 3.3mA and the remainder is divided roughly equally between the other nine circuits (0.5 вЂ“ 1.5mA each). The RCD operation seems to be good with all circuits disconnected it passes the no-trip test at 0.5I-delta-n and the disconnect times are 15.6ms and 11.1ms at I-delta-n and 5I-delta-n respectively ramp test shows that the RCD trips at 23mA.Д®arth leakage current (measured with an earth leakage clamp meter around the tails) with all MCBs closed and the installation вЂњas foundвЂќ (i.e nothing explicitly turned on or off) is 17mA. There are no obviously faulty accessories or equipment and the installation is generally in good condition. Insulation resistance test of the whole installation (L & N to E at 250V) gives 37kohms. (2) RCD trips very occasionally when garage lights (5x fluorescent tubes) or tumble drier are turned on вЂ“ this is much less frequent than the random tripping described in (1).Д®arthing Conductor and Main Equipotential Bonding all present and correct.ДЄll circuits have Zs within spec, measured at far ends of circuits. This has been happening since the customer moved in six years ago.

Tripping has occurred in all weather conditions but more often in stormy weather. On average the trip occurs once every two weeks, but a month could go by with no trips then, for example, it may trip three times in a weekend. (1) RCD Main Switch trips intermittently, randomly (i.e not coincident with equipment or appliances switching on/off, often when no-one is home), infrequently but frequently enough to be a real nuisance as it disconnects the whole installation. Here are the detailsвЂ¦ДЁ0A Main Switch/30mA RCD combined (MK 7880s) feeding 11 MCBs i.e a single 30mA RCD protects all 11 circuits, date fitted estimate 1990. IвЂ™d appreciate some opinions on my diagnosis and thoughts on a solution that will guarantee to fix the problem and also be cost-effective. Hi All, IвЂ™ve recently started out and have my first customer with an intermittently tripping RCD and relatively high earth leakage current.

Earth leakage unit