GFCIs are fairly simple devices. They have a current transformer with both line and neutral windings on the primary side. The secondary goes to the GFCI's trip circuit. As long as line and neutral balance, the output of the transformer is zero. If line and neutral don't balance, the output triggers the trip circuit. The GFCI doesn't directly measure leakage current and doesn't even require a ground connection to work. It works under the assumption that if line and neutral don't balance, the missing current must be leakage current.
The devices typically don't have a low-pass filter in them. They are designed to be simple and cheap. UL 943 is the safety standard for GFCIs, and it uses the human body model for leakage current. However, the tests are done with a 60 Hz sinusoidal current. There is nothing in the standard that prohibits GFCIs from detecting higher frequency currents. The transformer used only has a few windings on the primary, so it is probably efficient at high frequency current than low frequencies. As such, it may cause the GFCI to trip at lower levels of high-frequency leakage current than 60 Hz current. UL 943 does include tests for resistance to environmental noise using a 10 - 450 MHz signal source. However, if you have significant leakage current at high frequencies, it will still cause a trip. As bad as the technical issues are, they are more straight forward than dealing with the AHJ. A damp location is defied in the code as "locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture." This gives a lot of leeway to the AHJ in how they determine what constitutes a damp location. I wouldn't suggest arguing whether or not this is a damp location. Instead, stress that the equipment has a reliable ground. Your plug and cord provides a reliable, low-impedance ground connection. Any leakage current will reliably be carried away in the equipment's ground. GFCIs are generally required in residential installations due to the possibility of faulty grounds or the use of pluggable equipment without a ground. GFCIs are generally not required in industrial locations where equipment is reliably grounded. Ted Eckert Compliance Engineer Microsoft Corporation [email protected]<mailto:[email protected]> The opinions expressed are my own and do not necessarily reflect those of my employer. From: Kunde, Brian [mailto:[email protected]] Sent: Monday, April 16, 2012 7:06 AM To: [email protected] Subject: Re: GFCI for 230VAC Products We provide a 30 amp twistlock plug with the product and specify to use a dedicated circuit. What is the definition of an "Indoor Wet Location"? Our equipment is categorized as "laboratory equipment" which most labs have sinks in the area. We had this same problem a few years back with a 115VAC version of this same product. Our customers would plug our product into a standard GFCI receptacle but it would trip as soon as the frequency drive started up the motor. But then we found out that in 2006 the requirements for GFCI changed. We went to Lowes and purchased a new GFCI that said (UL 2006) right on the box. This GFCI worked fine and did not trip. We assume the 2006 version is less susceptible to high frequency currents. Whatever requirements changed in the 115VAC GFCI receptacles in 2006 did this also change for 230VAC GFCI breakers? Maybe not? Is anyone familiar with this change? I went to Lowes yesterday and looked at the GFCI breakers they had for sale. None of them referenced UL 2006, or any date of any kind. I just received an email from Square D/ Schneider Electric. They said they are familiar with the problem and believe it is caused by high frequency leakage current in the KHz frequency range from the frequency drive. They are probably correct, but why does GFCIs sense high frequency current? They said their GFCI breakers meet the requirements. We are trying to work the our customer and their AHJ to see if there is an alternative to using a GFCI. Thanks for the replies. They have been most helpful. The Other Brian From: [email protected]<mailto:[email protected]> [mailto:[email protected]]<mailto:[mailto:[email protected]]> On Behalf Of Ted Eckert Sent: Saturday, April 14, 2012 11:28 AM To: [email protected]<mailto:[email protected]> Subject: RE: GFCI for 230VAC Products Hello Brian, The likely clause is NFPA 70 210.8(B)(6). This clause requires GFCI protection in indoor wet locations for buildings that are not dwelling units. It is likely that the AHJ is applying their own interpretation to this clause to require a GFCI for equipment with a fixed water connection. The concern of the NEC is that if equipment has a faulty ground connection, a nearby sink other water source could provide an alternate ground return path. A person could touch both the equipment and the sink completing the loop. However, this doesn't make as much sense for equipment with a fixed water connection. You might be able to convince the AHJ that there isn't an alternate ground close by even with the water connection. If you require a copper water line, that may convince the AHJ that the equipment has a reliable alternate ground. EMI may not be the issue causing GFCIs to trip. I've run into this problem when using electronically speed controlled motors. Leakage current for safety is measured using the human body model, which measures AC current in the 50 - 60 Hz range. The circuit of IEC 60990 Figure 4 has a low pass filter formed by R1 and C1. Equipment may have higher frequency leakage current that is blocked by the test circuit but is high enough to trip a GFCI. I once had an air conditioner with an electronically speed controlled motor. A standard meter read a leakage current of 9 mA while the IEC 60990 Figure 4 circuit read about 2 mA. The equipment was safe, since the higher frequency currents were too high of frequency to interfere with the human heart rhythms. (The IEC 60990 circuit is designed to detect only the current that is harmful to people.) However, the GFCI looks at current of any frequency. If the problem is high-frequency leakage current, additional EMI suppression may not help. One option is to consider a locking plug for your product. If you supply your product with a NEMA L6-20 for example, it won't plug into a standard outlet. The NEC has a number of exemptions for equipment plugged into a circuit with a single outlet or to industrial locking outlets. The AHJ may consider the outlet as providing a reliable ground connection if it is a purpose installed outlet not serving any other equipment. Consult with the AHJ to see if there are conditions under which the GFCI will not be required. Ted Eckert Compliance Engineer Microsoft Corporation [email protected]<mailto:[email protected]> The opinions expressed are my own and do not necessarily reflect those of my employer. From: Bob Johnson [mailto:[email protected]] Sent: Friday, April 13, 2012 8:34 PM To: [email protected]<mailto:[email protected]> Subject: Re: GFCI for 230VAC Products You need to determine more carefully what requirements must be met. There are two different ground fault concerns in the code. Ground Fault Circuit Interrupters (GFCIs) are used for protection of personnel from electrical shock and are needed in wet areas. Ground fault protection of equipment is required for motor circuits but this protection is for the wiring and motor, not protection against electric shock. GFCIs are not necessarily required simply by the presence of plumbing. GFCIs are for protection of personnel from electric shock due to wet conditions. GFCI protection is generally required for receptacles due to the poor dependability of portable circuits and grounding. Only in some areas like pools are additional permanently installed equipments required to provide protection from shock. The NEC (NFPA 70-2012) requires GFCIs in the locations below. The code in effect is the one adopted by Tennessee which may be this or an earlier version of NFPA 70 and may have modifications. The GFCI and/or motor ground fault protection is usually part of the site installation done by the local electrician. That generally makes it a burden on the owner, not the product manufacturer unless the product codes require it to be built in. Which GFCI or motor protectors to choose would often depend on the brand of electrical panel involved. The following locations require GFCIs to some extent. There are exceptions and limitations. Sometimes 120V receptacles are required. Sometimes circuits must be protected. Bathrooms Garages Crawl spaces Unfinished Basements Kitchens Sinks Boathouses Boat Hoists Indoor wet locations Showers Garages Rooftops Outdoors Drinking Fountains Spray Washers Vending Machines Hydromassage Units Pools, Spas, Hot Tubs Fountains Marinas Bodies of Water Electric Signs Electrified parking spaces Elevators and lifts Space Heating Cables Construction Sites - Health Care Facilities Mobile Homes Recreational Vehicles Pipeline Heating Aircraft Hangers Bob Johnson ITE Safety<www.itesafety.com> On 04/13/2012 10:22 AM, Kunde, Brian wrote: Our company makes a 230VAC product (laboratory/light industrial) that has a water connection. We received word from a customer in Tennessee, USA, who says the NEC and/or the Tennessee Electric Code requires a GFCI be used with this product. We are not experts in the NEC so can anyone confirm this to be true? We did not know GFCI were required for non-consumer products. Our product uses a Frequency Drive to speed control a 2hp motor. EMI from the drive causes false trips in the GFCI. On a similar 115VAC product we found GFCI based on the 2006 requirements worked just fine as was immune to the EMI caused by a Frequency Drive, but we cannot find such a reference on 230VAC GFCI. Can anyone suggest a 230VAC 2 pole GFCI that is immune to EMI from Frequency Drives? Does the NEC allow for an alternative for a GFCI such as adding a secondary earthed ground bonding conductor or wiring the power cord direct? Thank you all for your help. The Other Brian ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
