old wiring vs. new wiring

[floby99]

i have a question for everyone. would i be able to hook up new romex wiring to old knob and tube wiring?

the reason i ask is because i am going to be changing a light from knob and tube wiring and im adding on two new plugs from it. would i be able to do this? and if so does the wire size matter?

 

[lectrishun]

Re: old wiring vs. new wiring

(NEC99)310-15(a) and 300-16(a) indicate that it is permissable and detail the requirements. I've found that the old K&T boxes have the required "separately bushed holes" as required by 300-16(a) but I must defer to someone more experienced in this area for more modern devices to meet this requirement.

G.

 

[bphgravity]

Re: old wiring vs. new wiring

Yes, 300.16(A)and (B) must be followed for the transition, and the wire size will have to be used that meets the rating of the OCD protecting the circuit.

 

[don_resqcapt19]

Re: old wiring vs. new wiring

In my opinion you are not permitted to install a receptacle on an extension of a branch circuit that does not include an equipment grounding conductor unless you install an equipment grounding conductor per the rules in 250.130(C). The points are which you are permitted by 250.130(C) to connect a separate equipment grounding conductor at are all at or near the electrical panel. If you can fish a grounding conductor back to the panel you could fish a new branch circuit and that is what you should do.
Some will say that 406.3(D) would permit you to install GFCI receptacles at the new locations. 406.3(D) only permits you to replace existing receptacles on a two wire circuit with GFCI protected receptacles. It does not permit you to install new receptacles on an extension of an existing two wire circuit.
Don

 

[jxofaltrds]

Re: old wiring vs. new wiring

Don

250.130 does allow for "branch-circuit extentions".

Why I would not allow an extention would be per 220.3(C)(1)(2).

Also 300.3(B) & 90.1(A).

I have a problem with part of the circuit having a ground and part not.

Can these old systems having shared neutrals make it difficult to add to the exsisting circuits?

Mike P

 

[don_resqcapt19]

Re: old wiring vs. new wiring

Mike,
I'm assuming that this is a dwelling unit and there is no added load calculation for receptacles. 300.3(B)(3) would clearly permit the extension of K&T circuit, as does 394.10. I see no problem with 90.1(A). K&T that has not been modified and was originally installed by a craftsman is a safe wiring method. Its biggest drawback is the lack of an EGC. It would be very unlikely that an unmodified K&T installation would have a shared neutral as most services were only 120 volt when K&T was being used.
Don

 

[jxofaltrds]

Re: old wiring vs. new wiring

Don

I too assume residential.

How do you read 220.3(C)(1)(2)?

Your ref to 300.3(B)(3) takes me to 332.31.

Can someone explain 332.31?

No EE here. Always learning.

mike p.

 

[al hildenbrand]

Re: old wiring vs. new wiring

Mike,

The handbook has the following after 332.31

Section 332.31 permits Type MI cables to be used as single conductors. The larger sizes of Type MI cable are available only as single-conductor cables. Because single conductors in a metal sheath can result in induced voltage on the sheath, this section requires all conductors of the circuit to be grouped together to minimize the voltage on the sheath.
Where single conductors enter a ferrous metal enclosure, inductive heating can occur due to hysteresis loss caused by the magnetic flux occurring in ferrous metals and I2R losses from the currents induced by the conductor. To minimize this magnetic heating of enclosures, 300.20 requires additional measures, including cutting slots in the metal between the individual holes for each conductor connector. Cable manufacturers offer nonferrous connecting plates that accept individual threaded connections of all circuit conductors, thereby eliminating circulating currents and fully complying with 300.20.

 

[al hildenbrand]

Re: old wiring vs. new wiring

Mike,

If I might take a stab at 220.3(C)(1)(2).

That, of course, leads to 220.3(A). Go down to Dwelling units and note the superscript ?. Go to ? after Table 220.3(A) and you will be sent to 220.3(B)(10).

The upshot, in a dwelling unit, on a General Lighting Load Branch Circuit, there is no limit to the number of receptacles that can be on an individual circuit.

This certainly may not result in a practical installation that can be lived with by the occupant, but its NEC compliant.

 

[don_resqcapt19]

Re: old wiring vs. new wiring

Mike,
Al has coverd the "additional load" issue. As far as 300.3(B)(3), you are reading too far. Stop after the first sentence. "Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B)." We are not using not using MI or MC cable in this application, so the last part of the section does not apply to this installation.
Don