Low and High Voltage Shared Termination Points

[fwood]

I have a question concerning cable termination requirements for low voltage and high voltage lines and their termination points. The college I work for has recently installed Code Blue Emergency Phones at all of its campuses and a question has come up concerning the terminations of the low and high voltage lines for these phones, naturally the question was raised after the project was completed. One of our Telephone Technicians, retired US West, went to check one of the units for dial tone. While checking this unit he found that both the high voltage (110 volts) and the low voltage wires (voice) co-occupy the last five feet (5?) of space. For each phone two separate conduits are installed; one for low voltage and one for high voltage. The conduits for voice (low voltage) are home run from our MDF Rooms to the base of the poles the phones is mounted. The conduits for the electric lines (110 volts) are home-run from the nearest electrical box to the base of the pole the phone is mounted on ? both conduits end at the base of the pole the Code Blue unit is mounted on. Starting at the base of the pole both low and high voltage lines start to occupy a single area, the pole itself, which is against code, according to our technician

In each phone the voice line terminates in an RJ11 and the electrical lines terminate to an exposed screw posts (no covers over the screw posts), which are located a few inches above the voice line. The area of termination is dark and small and requires the technician to reach into the enclosed area, blindly.

As I stated, our technician has indicated this does not comply with the Electrical Code and would like these units to be in code. This is where I get lost ? I have completed some searches for information concerning this matter and have not been able to find any answers or codes ? Wanting to comply with all Electrical Codes I need to find them first - Can anyone help, or point me in the right direction?
I would appreciate any assistance provided.
Thanks - Frank

 

[tom baker]

Re: Low and High Voltage Shared Termination Points

Can't share the raceway, see 800.52(A)(1), the voltage rating of the conductors does not matter, see 90.3, just in case some one quotes 300.3(C)(1).

 

[mkoloj]

Re: Low and High Voltage Shared Termination Points



[ February 11, 2005, 09:29 AM: Message edited by: mkoloj ]

 

[jrdsg]

Re: Low and High Voltage Shared Termination Points

this is suprisingly common in my experience.

one site that stuck in my mind is a large yard in which the electrical contractor had been instructed to install separate underground conduit to light standards on which cameras were to be mounted. there were indeed two conduits installed to each pole, but at the bottom of each pole these two conduits emerged in a common vault, then diverged again into two pipes that fed into the bottom of the pole. at this point there was again no separation, since the pole served as a common chase for lighting power and copper cctv power and signal cables.

i have seen similar installations frequently over the course of my dozen years in the business.

not only is there a safety issue involved, but there can also be inductance interference between high voltage and signal circuits. one would think that manufacturers of mixed-voltage appliances, such as the intercom stations in the first post, would make allowance for this in their designs.

[ February 11, 2005, 08:23 PM: Message edited by: jrdsg ]

 

[planas]

Re: Low and High Voltage Shared Termination Points

I have used a new hybrid cable named Simtra that allows power and data to be pulled in the same conduit in several of my projects. The power cable consist of a barrier that complies with NEC section 800.52 (A)(1)and is U.L. approved. This barrier absorbs the EMI and prevents distortion to the data cable.

 

[johnj]

Re: Low and High Voltage Shared Termination Points

I may be wrong, but it seems that 800.52(c), exception 1 & 2 addresses that. As long as the wiring is for the same system. Also 725.55 (B) through (J)

 

[frankc]

Re: Low and High Voltage Shared Termination Points

Some fire alarm power supply manufacturers specify spacing of at least .25 inches from power limited and non-power limited conductors. They also talk about different classes of conductors entering an enclosure from different knockouts.
I've seen NAC circuit cables shoved in to a box in the same conduit as 110 VAC power leads.