Keithley 2420 Sourcemeter trips GFCI - Page 1
Forum section: electronics / testgear

author: forrestc
author_rank: Unknown
timestamp: July 15, 2021, 10:21:28 am
content: So, I'm wondering if this is normal behavior for this instrument, or if I need to play 'what has failed in the filter circuit' games with this instrument.I have a new-to-me Keithly 2420 sourcemeter.For various reasons, I have chosen to protect my bench circuit with a GFCI, mainly so I don't kill myself when I stupidly stick my finger into the wrong spot in some device I've got open. I have enough exposed AC floating around often enough that I really prefer to continue to have the entire bench protected in this way.The GFCI doesn't like the 2420. It trips as soon as it's powered on. The instrument works normally in a non-GFCI outlet.I'd obviously prefer that this didn't trip the GFCI.Before I tear into this device and try to replace the AC filter caps (or module), I'd like to know if this is normal behavior for this device. I've had a couple of devices that just normally have some leakage current at startup which can't really be fixed by the normal method of replacing filter caps.Does anyone have this (or a similar) device and can tell me if this is normal (but obviously still undesireable) operation of this device?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 15, 2021, 10:33:33 am
content: It should not be normal for such a device to trip a GFCI. I know 2 types of appliences were it can be more likely to trip a GFCI: one are high power inverters for variable speed motors. To filter out the EMI they may need excessive filter caps and may sill produce high interfrence levels that can also cause trouble with some GFIs. The other class are high power / high temperature electric heaters. These may have a higher leakage current to ground and need a less sensitive GFI.My guess would be a broken EMI filter. So even if not causing problems on another outlet one should have a look.

author: Kean
author_rank: Unknown
timestamp: July 15, 2021, 12:42:50 pm
content: I agree with Kleinstein, not normal on this type of equipment. I usually only see this on faulty equipment, or if I forget to use an isolating transformer with some EMC test gear (LISN or AC transient generator).I assume "new-to-me" means it is out of warranty, and not yet valued enough for a proper service?You could try bypassing or swapping the EMI filter as a quick test as that would also be my suspicion. They are unfortunately one of the more common things to fail in quality equipment.

author: forrestc
author_rank: Unknown
timestamp: July 15, 2021, 11:45:21 pm
content: Quote from: Kean on July 15, 2021, 12:42:50 pmOk, I'll start digging into this.The main reason I asked is that I do have a couple pieces of equipment which specifically state in the documentation that they will cause GFCIs to trip, and they do, in fact, trip GFCIs. The one I know for sure is the VXI mainframe which is in use in the manufacturing line. I mainly wanted to make sure this wasn't a known shortcoming of this product.I'll also check into the cost of sending this in for repair. I also plan on having it calibrated so it might just be cheaper to do this in an all-in-one-go.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2021, 07:58:01 am
content: The main suspect for a fault is the EMI filter and this is a well defined part and often easy to replace and not a specific part.I would not expect test instruments to trip the GFCI on there own. There is a small chance to get such trouble in enenvironment with a high interference level (e.g. near an AM radio station, high power inverters, low quality PV inverters). Some of the EMI filter caps can than cause ground current and the combination of many electronik instruments may than combine to trigger the GFCI.In many regions GFCI protection is required for normal outlets, with only a few exceptions. Some industrial equipment may get away with a less sensitive GFCI. There are different classes of GFCIs, especially in how they handle DC and asymetric faults.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 16, 2021, 09:45:59 am
content: Turning the plug around usually helps. Something with mains inputs filters and switching neutral.