Brian
Thanks Grounding Conductors - what you have identified in C22.2 No 0.4 seems to largely confirm and expand on what I surmised from TN-017 and the related references. Regards John Allen W.London, UK -----Original Message----- From: Brian Oconnell [mailto:[email protected]] Sent: 05 May 2015 19:40 To: [email protected] Subject: Re: [PSES] Wire Questions CSA-C22.2 No 0.4 (Bonding of Electrical Equipment) has this 3.4.3.2 The fault capacity of a bond shall be adequate if the bond complies with one of the following requirements: (a) the bond is made from a suitably terminated conductor not smaller than the specified minimum size of bonding conductors in Table 16 of Part I of the CEC; Note: When equipment contains two or more motors connected to a circuit in the equipment that does not have overcurrent protection, the bonding conductor size is selected by assuming that the branch circuit protection is equal to three times the full load current of the largest motor plus the current required by the other loads. (b) in cord-connected equipment, the bond is made from a suitably terminated conductor not smaller than the bonding conductor in the supply cord; (c) the bond is made from a copper conductor not smaller than the applicable minimum size specified in Table 1 and meets the test requirements specified in Clause 4.1; (d) the bond is made from a conductor smaller than that required in Item (b) or (c), or smaller than required in Item (a) for overcurrent protection rated 40 A or more, and meets the test requirements specified in Clauses 4.1 and 4.3; or (e) the bond is made from a conductive element, other than a conductive element specified in Items (a) to (d), that meets the test requirements specified in Clauses 4.1 and 4.3 And table 1 indicates: Rating of branch circuit Minimum bonding conductor size, AWG required for equipment, A 15 20 20 18 30 14 Note that the 20gauge wire contradicts some stuff in NEC article 250(NFPA70), and CEC Part II (CSA C22.2 No 0-M9). Brian From: John Allen [mailto:[email protected]] Sent: Tuesday, May 05, 2015 11:09 AM To: [email protected] Subject: Re: [PSES] Wire Questions Brian Grounding Conductor size An interesting question with respect to internal grounding conductors, and one which made me refer to a very old copy of CSA Technical Note TN-017 “Bonding and Grounding of Electrical Equipment (Protective Grounding)”, dated January 13, 1993, which I have – don’t know if there is a newer version, but I suspect there is (if so, does anyone have a copy of this or of whatever has replaced it?) so the following comments may well be out-of-date! TN-017 refers to CSA C22.0.4, which I don’t think I have, as the basic requirements for grounding of equipment, so obviously not sure what that currently states. However: Page 2 of TN-017, under “Grounded (Class I) Equipment” states that “IEC standards require the ground path impedance to be less than or equal to 0.1 ohm. Although it is a satisfactory criteria for evaluating a path to ground where overcurrent protection is rated or set at 15A and 20A, this approach fails to provide proper protection when overcurrent devices are rated or set at 30A or higher” Page 6, Under “National Electric Code (NEC)” states: “Article 250 of NEC defines grounding and bonding requirements for installations of electrical equipment in the United States. Articles250-60, 250-95 and 250-155 also define min size of ground conductor required. Also see Articles 250-42, 250-45, 250-59, 250-113 and 250-114. NEC requires the following in particular. (a) Ground conductor must not be smaller than specified in Table 250-95 with the exceptions that the ground conductor: i. Must not be smaller than 18A AWG copper and not smaller than circuit conductors. ii. Need not be larger than the AC circuit conductors. This means that the min cord size permitted is No 18 AWG, and min size of ground conductor shall be No 18 AWG. (b) Ground conductor may be without insulation but if insulation is provided, it shall be coloured green or green with one or more yellow stripes. (c) All non-current carrying metal parts of fixed, portable and mobile equipment shall be grounded. Grounding conductors not part of cable assembly must not be smaller that No 6 AWG.” NB: w.r.t. (c) above, there are exceptions elsewhere for double-insulated (etc.) equipment! Can’t find any definitive statement in TN-017 as to the required internal grounding conductor sizes, but, from the above, it seems to me that the issue you mention relates to a combination of the following: - The IEC continuity test at 25A is only adequate at supply currents which would be protected by a 15A/20A external breaker, which is probably why 61010-1 states different – see below; - the potential AWG size of the external supply cord – and that the grounding conductor needs to be > the size of the current-carrying conductors; - the current rating of the protection in the installation – and if the latter is >15A/20A, then the internal conductor would have to be larger than 18AWG. Since you were using a 16AWG power cord in some cases, then that would mean the internal conductors would need to be >16AWG, but if you were sometimes using 14AWG cords – which you comment implies - then you would need 14AWG internal grounding conductors. OTOH, some more modern standards like 61010-1 Ed 3 state: 6.5.2.4 Impedance of PROTECTIVE BONDING of plug-connected equipment …..Conformity is checked by applying a test current for 1 min and then calculating impedance. The test current is the greater of a) 25 A a.c. r.m.s.at RATED MAINS frequency or d.c., b) a current equal to twice the RATED current of the equipment. If the equipment contains overcurrent protection devices for all poles of the MAINS supply, and if the wiring on the supply side of the overcurrent protection devices cannot become connected to ACCESSIBLE conductive parts in the case of a single fault, the test current need not be more than twice the RATED current of the internal overcurrent protection devices… So, if you had had suitable internal all-pole protection in the equipment, then something smaller than 14AWG might be acceptable to such standards. OTOH, anybody, please feel free to correct or update any of my comments above as you are probably in a much better position in the US/Canada to know the reality of the current (sic!) situation! Power Cord Sets As for European use of US cordsets, very few suppliers can supply actual cords with both US/CSA and third-party EU certifications due to the differences in the relevant UL/CSA and the IEC/EN standards – I think I only ever found one that had a limited range available (and, even then, it might only have been for extension cord sets or “Jumper Cord Sets” – not main supply cords), but cannot now be sure which one that was. However, unless the equipment was being submitted to a European test house for certification (or to some other company to incorporate in their own equipment), then it’s probably doubtful if the use of US/CSA-certified mains supply cords would be picked up by most of the end-user community. As long as the plug was the correct one, and the conductor insulation colours were also correct if an unterminated power cord was supplied, for those countries then most of those people would probably not look much further! Not to say that this is “right”/ “legal”, but taking a “pragmatic” view of the actual situation in most countries. ☺ Therefore, in the circumstances, it may well be better (as you appear to do) to leave the supply of appropriate power cords to the European installers! John Allen W.London, UK From: Kunde, Brian [mailto:[email protected]] Sent: 05 May 2015 16:37 To: [email protected] Subject: Re: [PSES] Wire Questions Rick, Are you talking strictly about power cordage or internal hookup wire? We had a CSA inspector reject one of our products because the internal PE Conductor (hookup wire) was a smaller gauge (18awg) than what was on the power cord (16awg). He said in Canada, the PE Conductor inside our product had to be the same gauge or larger than the PE conductor in the power cord regardless of the protection device or the current rating of the wire. In our case, we were using a 16 awg detachable power cord with an IEC 60320 connector. Inside our instrument, from the IEC connector to our chassis ground we used an 18 awg green/yellow hookup wire which can handle way more fault current than the 16 awg power cord. So as a general rule, we always use 14 awg hookup wire on IEC connectors just to be on the safe size; As such power cords can come in 18, 16, and 14 awg sizes. Our power cords for North America always have UL and CSA, but no CE or “harmonized” (at least it is not required to have this). When products are shipped to Europe I understood that UL/CSA cordage was acceptable (you still have to change the plug) as long as the conductor size met the requirements. That is why we don’t use 18 awg power cords anymore. I really don’t know the details because this is handled by our installers during the customer installation. Hope this was helpful. The Other Brian From: Rick Busche [mailto:[email protected]] Sent: Tuesday, May 05, 2015 10:08 AM To: [email protected] Subject: [PSES] Wire Questions We manufacture a product that is intended for both the US and Canadian markets in addition to the European community. Our wiring is currently UL/CSA and “harmonized”. Looking at the various wire vendors there are UL/CSA & CE certifications and certifications that are UL/CSA, CE and Harmonized. Is it acceptable to have wiring with just UL/CSA and CE? Also, I remember years ago a document or standard that stated that a grounding wire could be smaller than the load wires. The argument was that it doesn’t have to support the load but just fault the input current. Does this sound familiar to anyone? Thanks Rick - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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