2mA of current between dishwasher housing and earth. - Page 1
Forum section: electronics / general

author: Creep
author_rank: Regular Contributor
timestamp: October 31, 2018, 12:20:58 pm
content: Hi everyone! Ran into a bit of an issue yesterday and hoping some of you EE folks could help me out.So I live in and old soviet apartment building with all the wiring beeing without a ground wire.Yesterday I installed a dishwasher in the kitchen and upon touching both the dishwasher as well as and electric oven (they are both side by side) my arm got an electrical shock (the whole arm felt somewhat werid all evening long). The oven is physically touching the central heating system water pipes (both painted so I'm not really sure if there was any electrical connection between them at the time).Bringing out my trusty multimeter I measured 120V between the dishwasher casing and the water pipes, so I figure that it has class Y capacitors installed between power lines and the casing. The meter in capacitance mode measures 38nF between the ground prong and both of the power lines.Measuring the leakage current between the casing and the heater pipes I got a whooping 1.8mA AC, well in the "I should be able to feel that" range.So I have two questions here:1) Is so much leakage normal for a kitchen appliance? If not, what could cause this? The dishwasher is brand new.2) Any tips on dealing with the issue without replacing the wiring in the entire apartment? Would connecting the ground at the outlet to the heater pipes be considered safe practice?Any help would be much appreciated!

author: digsys
author_rank: Unknown
timestamp: October 31, 2018, 12:35:27 pm
content: Just to start the replies - most earth leakage systems (which go by various other names) trip at between 20-30mA !! so 2mA is WELL under that.It is considered that <20mA leakage is not enough to kill you, and MANY appliances, especially dishwashers / clothes washers etc can can be quite high.Heat + hot water / steam etc.Saying all that, without a REAL earth, you are relying on 2 neutral returns (with their caps), so what you found may not be unusual.To figure out a remedy, you'd need to work out exactly Live / neutral paths etcIt is also likely that the metal water pipes are acting like arealseparately referenced earth.Others with a better knowledge of soviet wiring will have helpful suggesions.

author: Ian.M
author_rank: Super Contributor
timestamp: October 31, 2018, 12:52:57 pm
content: The problem with bonding to the pipes in a multi-occupancy building, is you cant be certain they will continue to provide a good low impedance ground (or if they even do to start with). 1.8mA leakage current to protective ground or the casing isn't dangerous, but if a significant number of appliances get their protective ground connections wired in parallel without a true low impedance ground connection, the total leakage current could become dangerous. It doesn't take many apartments grounding several appliances in each to the pipes to get up to a dangerous leakage current, and as each apartment presumably has its own breaker panel any RCDs (aka: GFCIs or ELCBs) probably wont trip as each only 'sees' a small part of the total leakage. Then along comes a plumber who uses a length of plastic pipe to repair a leak in the rising water main, and every floor above that point looses their low impedance ground connection. Then all it needs is enough water on someone's kitchen floor to soak into the concrete and make a low impedance path to the rebar in the building structure and you have a potentially lethal shock hazard.The appliance in question is unsuitable for operation from an ungrounded supply. Your only practical remedy is for a competent electrician to install an adequate grounding conductor, + equipotential bonding in your kitchen. There's no need to rewire the rest of the apartment, unless you want the benefits of grounded outlets elsewhere.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 02, 2018, 09:23:01 pm
content: Quote from: Creep on October 31, 2018, 12:20:58 pm1. This entirely depends on the complexity of the machine. But I believe 3.5mA is allowed for fixed machinery. (fixed machinery must always be grounded)2. Ground the dishwasher. And no, pipes are not intended to function as grounding. Someone could die when they only cut the pipe when a fault current is present.

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 02, 2018, 09:31:38 pm
content: There definitely should not be 120v between appliances let alone enough to feel a shock! Everything should be at earth potential. It sounds like there is a fault somewhere and the hot is touching the chassis. I would try to run a ground to it, even if you end up using the pipe as ground it's better than nothing... but ideally I would run a ground cable to the entry point of the pipe so it minimizes the chance of someone breaking that connection.

author: amyk
author_rank: Super Contributor
timestamp: November 03, 2018, 01:28:03 am
content: Quote from: Red Squirrel on November 02, 2018, 09:31:38 pmIf that were the case he would've been able to get far more than 1.8mA out of it.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 03, 2018, 01:59:03 am
content: Well, the question that comes to mind is how is your power brought to the building? Does your power company bring power and a ground to your fuse box? Are the transformers that bring your power to your building grounded at the pole or grounded at the building fuse box or both?I don't know anything about how Latvian power companies bring you power or even if there are rules governing this in Latvia. In the USA we have rules governing power input to buildings and homes, and I know how it is configured. If you have a pole ground only, this could explain why you have 120 volts to ground, but only a few millamps, depending on the type of soil, the moisture content, etc., V=IR, or in this case, I=V/R.AS far as telling you whether you should connect a ground or not connect a ground, the unforeseen circumstances can create some undesired effects. Without knowing all of the facts it is impossible to give good advice.Sorry for the lack of a good answer...

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2018, 11:03:46 pm
content: I wired in my dishwasher through a GFCI. It has yet to trip. In operation like 3 years now.https://www.ecmag.com/section/codes-standards/dishwasher-gfci-protection-cee-length-and-moreThe old iron curtain countries have terrible electrical. I was in one recently where there was like 1 transformer per 20-30 houses. It was normal to dim the whole house lights from a microwave oven turning on. I wanna bet the neighbors know when your reheating pizza.