Originally Posted By: jtedesco
This post was automatically imported from our archived forum.
http://www.nachi.org/bbsystem/viewtopic.php?t=5227
--
Joe Tedesco, NEC Consultant
www.nachi.org/tedescobook.htm
http://www.nachi.org/bbsystem/viewtopic.php?t=5227
Originally Posted By: dbozek
This post was automatically imported from our archived forum.
Ok I will give this a try…
The egc should be at both disconnects and should be bonded to the enclosure. How's that?
Let's say......for instance, one of the legs of ac shorts to the disconnect enclosure 
Would that protection device for the ac trip?
Chances are it would not without a egc bonded to the can.
Let's go a step further and say.....the house has aluminum siding on it and the ac disconnect is connected directly to it. In the above scenario....what would happen if Mr. Homeowner leaned against the siding with his bare bod.....with no egc at the enclousre 
Without the proper grounding of this appliance, the results could be quite shocking.
Therefore, the egc is required to bond the enclosure and ultimately, to bond the metal parts of the air conditioner, if in fact the egc is fed to the same.
Did I do ok Joe?
--
You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln
Originally Posted By: jtedesco
This post was automatically imported from our archived forum.
Dennis: OK, I think you done real good! and below see also the discussion on the question first posted in the link above:
The low voltage thermostat wires are not permitted to be run in the same cable or conduit because they do not have sufficient construction specifications to permit them to be installed with electric light, power conductors and any failure of the cable insulation due to a fault could lead to hazardous voltages being imposed on the thermostat circuit conductors.
The use of the same insulation for circuits up to 600 volts for both AC and DC is acceptable when run in the same cable or conduit, but not for this application.
It is better to see that thermostat wiring run in a separate cable or conduit, or wrapped around the cable or conduit that will supply the unit.
Please be aware that the subject of high and low potential is now referred to as Low and High voltage, with high voltage beginning at 601 volts and above.
--
Joe Tedesco, NEC Consultant
www.nachi.org/tedescobook.htm
Originally Posted By: dbozek
This post was automatically imported from our archived forum.
I agree with that Joe and for the reasons specified and as luck has had it for me, I’ve not witnessed that problem with air conditioning as of yet, but in this business all is possible
–
You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln
Originally Posted By: jpeck
This post was automatically imported from our archived forum.
| jtedesco wrote: |
| It is better to see that thermostat wiring run in a separate cable or conduit, or wrapped around the cable or conduit that will supply the unit. |
Not wrapped around the cable or conduit, that will act as a choke coil should there be a ground fault or high surge in the thermostat cable.
'Supported by' the other cable or conduit, provided it is not outside (unless the low voltage cable is one of the types allowed to be outside), not in the plenum unless plenum rated.
--
Jerry Peck
South Florida
Originally Posted By: jtedesco
This post was automatically imported from our archived forum.
| Quote: |
| Not wrapped around the cable or conduit, that will act as a choke coil should there be a ground fault or high surge in the thermostat cable. |
Jerry:
I would agree, if we were discussing the 6 foot maximum Equipment Bonding Jumper run on the outside of a raceway, because there was a change that supports the "routed with" instead of "routed around" that was accepted some time ago, anyway I would like to learn more about your scenario and the choke coil and if you are recommending that we be on the lookout for the thermostat wires that are wrapped "around" the conduit.
See 300.11(B) for language that does say support but doesn't say around or with ...
--
Joe Tedesco, NEC Consultant
www.nachi.org/tedescobook.htm
Originally Posted By: Greg Fretwell
This post was automatically imported from our archived forum.
I am a little curious about that “choke effect” too. Just exactly what problem might that cause?
In fact it might actually prevent a surge from smoking an electronic thermostat. We used to loop ferrite beads around our cables in the computer biz to stop transients and common mode noise.
The effect on 60hz is negligable.
On the other hand we never put a loop in a bonding conductor if we could avoid it, just so the transient had a straight path to ground.
Originally Posted By: MarK Heller
This post was automatically imported from our archived forum.
No proper ground at either unit. This could lead to hazardous voltage on the cases, and other associated metalic extentions of the equipment. (like reffer lines) If a fault were to occur. Some NEC and commentary.
| Quote: |
| 250.134 Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed) ? Grounding.
Unless grounded by connection to the grounded circuit conductor as permitted by 250.32, 250.140, and 250.142, non?current-carrying metal parts of equipment, raceways, and other enclosures, if grounded, shall be grounded by one of the following methods. Section 250.134 eliminates any conflict between 250.134(A), which requires an equipment grounding conductor to be used for equipment grounding, and 250.32, 250.140, and 250.142, which permit the grounded circuit conductor to be used for equipment grounding if certain specified conditions are met. (A) Equipment Grounding Conductor Types. By any of the equipment grounding conductors permitted by 250.118. (B) With Circuit Conductors. By an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors. One of the functions of an equipment grounding conductor is to provide a low-impedance ground-fault path between a ground fault and the electrical source. This path allows the overcurrent protective device to actuate, interrupting the current. To keep the impedance at a minimum, it is necessary to run the equipment grounding conductor within the same raceway or cable as the circuit conductor(s). This practice allows the magnetic field developed by the circuit conductor and the equipment grounding conductor to cancel, reducing their impedance. Magnetic flux strength is inversely proportional to the square of the distance between the two conductors. By placing an equipment grounding conductor away from the conductor delivering the fault current, the magnetic flux cancellation decreases. This increases the impedance of the fault path and delays operation of the protective device. |
The same for the thermostat wire. As Joe mentioned, NOT allowed IN the conduit, but may be on only the conduit associated with the AC unit. ( from the disconnect to the unit)
| Quote: |
| 300.11(B) Raceways Used as Means of Support. Raceways shall only be used as a means of support for other raceways, cables, or nonelectric equipment under the following conditions:
(1) Where the raceway or means of support is identified for the purpose; or (2) Where the raceway contains power supply conductors for electrically controlled equipment and is used to support Class 2 circuit conductors or cables that are solely for the purpose of connection to the equipment control circuits; or (3) Where the raceway is used to support boxes or conduit bodies in accordance with 314.23 or to support luminaires (fixtures) in accordance with 410.16(F) The purpose of 300.11(B)(3) is to prevent cables from being attached to the exterior of a raceway. Electrical, telephone, and computer cables wrapped around a raceway can prevent dissipation of heat from the raceway and affect the temperature of the conductors therein. This section also prohibits the use of a raceway as a means of support for nonelectric equipment, such as suspended ceilings, water pipes, nonelectric signs, and the like, which could cause a mechanical failure of the raceway. However, 300.11(B)(2) does allow the installation of Class 2 thermostat conductors for a boiler or air conditioner unit to be supported by the conduit supplying power to the unit... |