Cat6 Phone and door bell

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don_resqcapt19 said:
It doesn't have to be dual rated. Type "CM" is a permitted sub for type "CL2". See Table 725.154(G).
Click to expand...

I see it. It's table 725.61 in the 2005 NEC and 725.56 (D) permits class 2 in the same cable as art 800 circuits. I remember the cable I saw listed dual rated, it was 18-2 dual listed CMP and CL2P, and had a substantially upgraded insulation over regular thermostat wire.

Another table to look at is chap. 9 table 11 (A), which lists class 2 circuit power ratings up to 8 amps and 100 va. That's what the CL2 rating gets you, it says it will carry the power levels of the class standard, which are commonly runs of 200 ft or so, and pull in the coil of a DP contactor or power the gearmotor of a Belimo motorized operator.

The code is there for standardization over millions of installations with very few problems. Do you think there is any blanket statement that CM rated 23 ga cat 5 can be substituted for class 2 power carrying circuits. Can guys run building control circuits and treat cat 5 like a 4 pair CL2 circuit. No, not in a standardized way, it will have a high incidence of failure to operate.

If you want to turn the doorbell circuit wiring into an exercise in field engineering, then yes, I agree, it is possible to do the numbers and limit the attached load to the power carrying limit of a pair of cat 5 23 ga, or paralleled runs of 23 ga, since art 725 is exempted from most of the chap 3 code requirements (minimum size to parallel).

To send crews out and tell then it's OK to sub cat 5 for CL2, the CL2 load va's are well beyond what cat 5 can operate at.
 
__dan said:
I see it. It's table 725.61 in the 2005 NEC and 725.56 (D) permits class 2 in the same cable as art 800 circuits. I remember the cable I saw listed dual rated, it was 18-2 dual listed CMP and CL2P, and had a substantially upgraded insulation over regular thermostat wire.

Another table to look at is chap. 9 table 11 (A), which lists class 2 circuit power ratings up to 8 amps and 100 va. That's what the CL2 rating gets you, it says it will carry the power levels of the class standard, which are commonly runs of 200 ft or so, and pull in the coil of a DP contactor or power the gearmotor of a Belimo motorized operator.

The code is there for standardization over millions of installations with very few problems. Do you think there is any blanket statement that CM rated 23 ga cat 5 can be substituted for class 2 power carrying circuits. Can guys run building control circuits and treat cat 5 like a 4 pair CL2 circuit. No, not in a standardized way, it will have a high incidence of failure to operate.

If you want to turn the doorbell circuit wiring into an exercise in field engineering, then yes, I agree, it is possible to do the numbers and limit the attached load to the power carrying limit of a pair of cat 5 23 ga, or paralleled runs of 23 ga, since art 725 is exempted from most of the chap 3 code requirements (minimum size to parallel).

To send crews out and tell then it's OK to sub cat 5 for CL2, the CL2 load va's are well beyond what cat 5 can operate at.
Click to expand...

CMP can substitute for:
Table 725.154(G) -- CL3P, CL2P, CL3R, CL2R, CL3, CL2, CL3X, CL2X
Table 760.154(D) -- FPLP, FPLR, FPL
Table 800.154(b) -- CMR, CMG, CM, CMX
Table 820.154(b) -- CATVP, CATVR, CATV, CATVX (using baluns, I guess)
Table 820.154(b) -- BLP, BLR, BL, BLX (NOT for BM, BMR or BMU)


So CMP covers 23 other cable type according to the NEC (2011).
I guess the "dual-rating" was a sales thing since CMP is automatically useable as CL2P.
CL2P is available as 22 and 18 AWG from Belden for example.
As always, electricians must choose a conductor size adequate for the load.
 
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In reply to FMTJFW, I think your test passed because you used a low current/high impedance Western Electric telephone buzzer instead of an ordinary doorbell which runs on a 20VA transformer? Try it again with a real doorbell and we'll see if it works as well.

After posting, I thought about adding the comment that Haydenjsle made about using a 'door phone'. I didn't know there was one that worked without a proprietary phone system? The only problem I see with this unit is that it does not appear to be safety agency listed for connection to the power OR telephone lines.:slaphead:
 
Jerry the Phone Guy said:
In reply to FMTJFW, I think your test passed because you used a low current/high impedance Western Electric telephone buzzer instead of an ordinary doorbell which runs on a 20VA transformer? Try it again with a real doorbell and we'll see if it works as well.

After posting, I thought about adding the comment that Haydenjsle made about using a 'door phone'. I didn't know there was one that worked without a proprietary phone system? The only problem I see with this unit is that it does not appear to be safety agency listed for connection to the power OR telephone lines.:slaphead:
Click to expand...

If I had a doorbell I would have used it. The original post posited 2 CAT-#s, one for telephone and one for the doorbell. I believe if you parallel all colored as a group and all the white as a group you get the equivalent of #16. That has lower resistance than #18 bell wire.

I purposely described the experiment in detail so others could reproduce it, or modify it. Have at it.:)

Thanks, Jim Williams
 
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