Chris,
There is an exception for connectors. It is in section 6.1.1). When the connector is mated, there must be sufficient creepage and clearance to satisfy the values from the table that has high voltages on it. These values are directly derived from IEC 664 values. I noticed the "grounded" connector shell. You mention that the cable is "screened". Do you mean that there is a braided copper shield that is between layers of insulation and that this shield connects to the shell and is returned to chassis ground ? If so with your source impedance of 150 Kohms, the shield should be well able to carry the 100 mA current from a short. (You might also review 6.9.1 for rules of construction in regards to how the braid is attached to the connector shell. It should not rely on solder alone !) Your creepage and clearance distance would then be "basic", otherwise you would need to increase the values in the table to comply with Double or Reinforced spacings. So under "Normal" operating conditions , (mated connector) the creepage and clearance must comply with the values from the table and linear interpolation is allowed for values between those in the table. Under "Single Fault"conditions, (unmated connector) the live end must be recessed as far as "feasible" (Amendment 2 to IEC 1010). The language of the exception clause (6.1.1) is under revision, but the intent is constant and consistent. The connector would be of no value if the live female receptacle were recessed so far that it could not make contact. The designer must do what is "feasible" or "reasonable" to protect the user, but connectors have voltage on them, just like meat cutters have sharp blades, neither is very useful otherwise. Hope I've been of some help. Dan Teninty PE HMSC Tucson, AZ ______________________________ Reply Separator _________________________________ Subject: HV connector safety. Author: Chris Dupres <[email protected]> at CCGATE List-Post: [email protected] Date: 3/11/97 8:16 PM Good Folk. A question re. interpretation of the Creepage and Clearance tables in IEC 1010-1. BS EN 61010-1 etc. The Facts: 1. I have a cable terminated with a female connector that carries 15kV to a fixed device (an electron gun on a vacuum system in this case). This is rather similar to a screened aircraft Spark Plug lead. 2. The cable is screened, and the connector is all metal (grounded) with a ptfe piece inside which supports the female contact, and provides an insulating sleeve up the inside of he connector body to provide the necessary clearance and creepage path lengths for reliable operation. 3. The ptfe inner does not extend all the way along the inside of the connector case, leaving a few mm of uninsulated (grounded) metal. 4. It is possible to put the IEC1010 Annex B Test Finger into the connector and to touch the live receptacle, but it is impossible to do this without grounding the Test Finger on the Connector case. The Question... Am I right in assuming that using the Test Finger to locate (IEC 1010 6.2.) and measure (IEC1010 6.3.) the voltage on the accessible part, then using the circuit in IEC 1010 Figure A.2. I will show that the actual volts measured will be zero, so under those conditions claim that the connector can be described as 'safe'? In reality, if someone was to put their finger into the connector and touch the HV contact, they would provide a current path to earth (the body of the connector) through their finger, and one that would effectively bypass conduction through their body to earth. The source impedance of the 15kV is approx 150Kohms. So, does providing an unavoidable earthed 'guard ring' at the access to the high voltage terminal provide protection such that the Creepage and Clearances required in IEC 1010-1 can be disregarded? What do you think folks, Reasonable? Sensible? Safe? or What? Your opinions are, as always, most valuable. Thanks Chris Dupres Consulting Engineer Surrey UK
