Will European Plug Still Be Earthed Through UPS Provided Only N and L Connected? - Page 1
Forum section: electronics / beginners

author: Boris_yo
author_rank: Frequent Contributor
timestamp: July 29, 2012, 03:10:57 pm
content: Will europlug that has that slot for a sockets with ground pin protruding from them still able to be earthed in a country that has different socket if connected through grounded UPS? In other words, if UPS is grounded per se but can only connect europlug's neutral and live without ground, will device that uses that europlug be still grounded?

author: bilko
author_rank: Frequent Contributor
timestamp: July 29, 2012, 03:12:45 pm
content: no

author: SeanB
author_rank: Super Contributor
timestamp: July 29, 2012, 03:39:00 pm
content: go and but a proper Israeli style plug and cut the French one off. The pins in any case are too big and will crack the socket with time.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: July 29, 2012, 07:17:01 pm
content: Let me clarify that UPS deviceISgrounded by itself as should be any appliance that is connected to UPS.

author: SeanB
author_rank: Super Contributor
timestamp: July 29, 2012, 07:26:17 pm
content: Unless you have a separate grounding connection there will be no grounding to the supply PE terminal. The UPS and the computer attached to it will have all exposed metalwork floating at half mains voltage, and at a current that is enough to give a bad shock at best. This is from the common mode filter capacitors in the UPS and the computer power supply, which are sized value wise on the assumption that there will be a mains earth present. You can easily have 100n of capacitor present in this case, and the current flow through you, should you be the path completing the earth circuit, can shock or kill you, or injure you.

author: bilko
author_rank: Frequent Contributor
timestamp: July 29, 2012, 07:33:00 pm
content: Quote from: Boris_yo on July 29, 2012, 07:17:01 pmYour UPS may well be grounded but unless your appliance also has its ground wire connected it is NOT grounded. On a 220V supply, it could float up to 220V

author: Kremmen
author_rank: Super Contributor
timestamp: July 29, 2012, 08:05:16 pm
content: Quote from: SeanB on July 29, 2012, 07:26:17 pmBasically correct except that at least in EU and i suspect elsewhere as well you cannot have so large a Y capacitance ( from L and N to PE) precisely because the permissible current is strictly limited to just a few mA. This in order to avoid safety issues as well as nuisance tripping the RCDs now mandatory in the code in many regions. The generally approved max value according to EN60335-1 and EN60950-1 for Class I portable equipment is just 0.75 mA resulting in 4.7 nF Y cap in most general purpose filters around. So you might feel a tingle and it might be unpleasant but it must not be life threatening. At least if the properly dimensioned Y class specified caps have been used.For Class I stationary the limit is 3.5 mA but that would not apply for something like a PC.

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2012, 05:01:02 am
content: UPS 4n7, PC 4n7, monitor 4n7, odd acessory power supplies and all those capacitances add up. Remember the capacitor across the isolated section for noise supression is generally 10n as well for most SMPS units.

author: Kremmen
author_rank: Super Contributor
timestamp: July 30, 2012, 07:21:14 am
content: Yes, of course they add up, as many times as you have gadgets connected to the supply. That is precisely why any one of them may not have arbitrarily large stray currents into PE. Still what is supposed to happen is that the RCD in a properly grounded installation will trip before a life threatening stray current can accumulate. Now, if you keep on adding into ungrounded supply devices that specifically require grounding means that at some point you will win the Darwin award. Not to do this will be printed in the safety instructions of the gadgets, that nobody ever reads (edit: meaning the instruction says " this equipment is to be connected to grounded outlet only yada yada"...).If by "across the isolated section" you mean between L and N (the X cap) then that won't cause any leakage into PE. Generally the only one that does so is the Y cap and during overvoltage surges, the MOVs or similar protectioon devices. Oh, sorry - there may be capacitive coupling from the secondary side of an SMPS to PE and that does not count against the RCD stray current budget. Offhand i cannot recall which standard governs that current. However, as that connection is galvanically isolated from the grid, it will not cause a (differential mode) current through say a person touching the device.

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2012, 03:25:49 pm
content: Normally a dedicated capacitor across the isolation barrier, either a class Y ceramic or 2 in series, depends on the manufacturer. There to reduce radiated noise from the transformer by decuopling it to the supply side capacitor positive or negative. Thus this is connected to the mains and has a current flow through it as well at mains frequency.

author: Kremmen
author_rank: Super Contributor
timestamp: July 30, 2012, 05:22:48 pm
content: Yes that is about what i meant by the part after "Oh sorry..." in my previous. If the caps are from the secondary to L or N it does not impact the stray current to PE because the currents still need to pass thru the original Y caps to get there. If directly to PE then again not as the secondary is isolated by the transformer. Only if you have both then a new path is available through the caps in series. Offhand i cannot recall ever seeing that kind of circuit.