Building Lighting as Drawn vs. as Installed 1

[SDestimator]

First, a bit of background info on myself. I am a 20 year journeyman electrician in Southern California. I was a foreman running jobs for a good part of that time. I recently took a position as an estiamtor for a mid-size electrical contractor.

My question concerns the way lighting systems in building interiors are drawn as opposed to how they are actually installed.

The vast majority of plans show lighting circuits routing form space to space via J-Boxes in ceiling spaces (or sometimes through the fixtures themselves). From these boxes or fixtures switchlegs are "dog-legged" down to switch boxes in the wall. I will get to some of the things I feel are an issue with this method in a minute.

On to how lighting systems are (usually) installed.

Most lighting systems are installed by feeding power directly from switchbox to switchbox then bringing switchlegs from the switchbox to the fixtures served (usually local to the space) by the switch.

Now the issues.

First, the cieling J-Box method of drawing makes for very cluttered lighting drawings. Routing the live circuits from switch to switch and the switchlegs to the fixtures served makes the intent of the drawings more clear in my opinion.

Second, using fixtures as landing points for unswitched circuits is less friendly fom a maintenance standpoint(granted there are times when it is necessary, such as emergency lighting battery charging circuits). If a fixture can be safely shut down at a local switch rather than shutting the whole lighting circuit down, there is less impact as far as possible interference with lighting in other spaces.

The one drawback to the switch to switch method is that the constant hot circuit can end up slightly less accessible for future changes. There are ways around this though (local J-boxes in the home-run circuit for instance), but the benefits to this method outweigh this drawback.

My question to Engineers is this: Is there a reason behind the ceiling J-Box method, or is it just convention?

 

[davidbeach]

A lot of it is probably convention, but running the phase conductor through every light switch box ensures that replacing a switch will take out lights elsewhere in the building, even if the work is done hot.

 

[SDestimator]

From an installers point of view that is incorrect davidbeach. NEC requires "pigtailing" of neutral conductors (see 300.13(B),2005 ed.), and this practice has carried over (at least from my experience)to all conductors where a splice occurs in a box which contains a device. In other words, the hot phase conductors that pass through the switch box are wirenutted together, and one single conductor is spliced in with them and attached to the device (in this case a switch). the switch can be swapped out without ever having to interrupt power to downstream devices (caution must be used of course, as the stripped portion of the hot conducter will be live). This is a simple operation which I have performed many times (generally during troubleshooting of a new installation).

 

[davidbeach]

Interesting, can you cite the code section that requires phase conductors to be pigtailed? I'm aware that a neutral conductor of a multi-wire circuit has to be pigtailed, but in many years of working with the NEC never was aware of a requirement that phase conductors have to be pigtailed.

 

[z633]

I thought it had to do with the efficient use of copper. Running HNG(3), and SH,SR(2) in out switchbox to switch box? I would think would use more length. Length = Voltage Drop. Maybe less labor?
Anyway, I now specify lighting control panels and the associated low voltage controls whenever possible.

 

[IRstuff]

From an end-user perspective, it means that I, who does not have a wiring diagram of my house, can't tell where power enters a particular room, and I have to be concerned about adding loads, since I have no idea where anything goes or comes from. Additionally, if I want to add a wall socket or additional load, I would have to break into an existing loop, rather than just tapping off the j-box.

Seems to me there would also be issues with the loading of the conductors. You'd have to run thick wire everywhere to make sure that any future wiring changes do not cause voltage drops or overheating of the conductors.



TTFN

 

[SDestimator]

davidbeach- NEC doesn't specifically say you must pigtail ungrounded conductors, but it does say terminals will "ensure a thouroughly good connection"(see 110.14(A), 2005 ed.). It is a hell of a lot easier to get 4 wires in a wirenut than it is to get those 4 wires under the single screw terminal on a switch . The same thing can be said for most receptacles. (residential work being something of an exception, but I don't do resi).

z633- I'm not sure there is enough difference in lengths as shown on a drawing between these two methods to make voltage drop the reason, but I can tell you most lighting systems I have seen installed route power from switch to switch, then run a switchleg (including a neutral and ground)up to local lighting fixtures. Some installers will place a J-Box in the ceiling directly above the switchbox for ease of future access, but power is still routed from switch to switch as opposed to fixture to fixture with "dog-legged" switchlegs(raceway with only the unswitched and switched hot going to and from the switch). I have seen inspectors (in error) violate dog legged switching because the raceway does not contain it's associated ungrounded and grounding (neutral and ground) conductors (there is an exception to this rule for switch loops).

IRstuff- As far as ease of determining where somethings power originates from without access to as-built drawings goes, there is not much difference between these methods.

Accessability after the fact is another story. I will once again maintain that most houses lighting gets wired switch to switch though, at least in my area.

The actual load on the conductors is a seperate issue from how a circuit is routed. You can overload a circuit after the fact regardless of conductor routing. That is the reason we have circuit breakers. You should always verify that you won't be overloading a circuit before adding additional load to it. Best bet is to hire an electrician .

 

[EEJaime]

Showing the circuiting running from room to room with drops down to the switches with hot conductors and switch legs back up is simply easier to mark up, draft and keep track of. Especially with CADD these days, I can do an entire school building by copying, mirroring and rotating a classroom lighting layout, then simply assigning a circuit number to the j-box in each classroom, regardless of the switch locations. It does not matter to us exactly how the circuiting is actually run as long as any changes from what is on the drawings, are picked up on the contractor's "as-built" drawings. Where we do insist on specific routing is where we use occupancy sensors, especially multiple circuit sensors,where power/relay packs are required, or where we have emergency lighting as we always carry an unswitched hot leg to power exit signs, battery packs, etc....

It is much easier to teach a junior designer how to circuit a lighting plan and keep the wire counts straight if we keep the representation on the drawings consistent.

 

[BJC]

I don't show the details of wiring on a drawing. Most electrican know more about running lighting circuits than engineers. The drawings should show where the switches are, which fixtures they switch and the circuit numbers.
Even those are subject to change in costruction. Doors get moved, walls added etc.
A good "as built" is allways handy. It will save work as soon as the first "TI" project comes in.
The only time I have had to minutely detail wiring is when we knew it was going to some open shop outfit whos "electricans" were lost when three pieces of romex came into the same box.
Engineers and good electricans are part of a good team. Engineers don't have to do everything (or even try).

 

[SDestimator]

EEJaime- Thanks for the input. Correct me if I'm wrong, but it seems to me that it is easier to keep track of which conductors need to be in which conduits if you aren't mixing hot circuits with switchlegs. Also, from an installers perspective it is much easier to As-Built something that was designed fairly close to how it will actually be installed. From an estimator's perspective it is easier to come up with an accurate bid if the drawings reflect actual construction methods. You could still cut and paste a room layout, with continuity of the power feed being from switchbox to switchbox. As a side note, the reliance on cut and paste in CAD has caused a serious degradation in the quality of construction drawings in the last 1o years in my (and many other construction professionals I know) opinion(s). It is a powerful tool when used correctly, but all to often it is abused and sloppy drawings that create RFI's that should not have been required seem to be the rule these days (sorry for the rant).

BJC- I have seen a number of drawings using your method. They have their advantages, but as you said, if you get a sub-par or unscrupulous contractor you could be in for trouble. Also, on larger or more technical projects I don't know how well this method would perform.

 

[rbulsara]

I will add my two cents.... this is not the comment as to how to show a lighting circuit but much looking at the bigger picture, even at risk of singing to a quire.

It would be helpful to understand the scope and responsibility of design engineers and contractors and the very purpose of design drawings as prepared by consulting engineers.

Drawings produced by engineer are Contract Documents that includes the requirements of a project so that a contractor can understand the scope of work and bid the job correctly and if successful in getting the contract can build the project as intended by the Contract Document.

The drawings that form part of contract document are not "installation drawings" that show how to the work, they only are meant to indicated what to do and what quality is desired (by specifications). Detail method or instructions are only included when the engineer wants certain task done a particular method.

As for the lighting circuits shown on such drawings are generally meant to indicate separation of circuits and to show which switch controls which group of lights and not to show the electrician how to wire it (terminal to terminal). It is not the case of who know more.

Contractors (electricians) are supposed to know more about construction methods and how to build and they may not always know what is best to build. Engineers are supposed to know what to build and be reasonably sure that what they want to build is constructible and what they specify is available.

Engineers devise solutions, contractors implement them, Owner pays!!!. It is a team work.

 

[EEJaime]

Very well put rbulsara, I agree with your analysis of the distribution of tasks in the construction industry. When working with highly experienced, professional Electrical Contractors, it is very easy to provide sufficient information for the work to be priced, procured and installed. It is when market forces push contractor's whom are not experienced in the fields they attempt to enter that things go south in a hurry. A contractor not used to installation in a hospital environment, or a public school, has no idea how difficult and demanding that installation is until we virtually have to stop construction to get him to comply with state agency requirements. Experienced contractors don't even need us to show detailed circuiting. I merely indicate switch locations, controlled loads for each switch, circuit and panel designations, and the contractor can put it together.

I do agree that CADD has been a double edged sword. I would say that 98% of all engineering cadd operators have never had a drafting class in their lives. My details come out as if drawn by Pablo Picasso. It is exasperating. I have come to insist on working with a select few of our operators whom know that if things are not drawn right, they will be drawn again. It's amazing to me that details I developed and drew about 25 years ago are still in our "Standards" book, and in many cases no one has bothered to update them. I frustrate many in our CADD department because I am "old fashioned" and insist that my drawings confer information while not appearing as if drawn by a three year old. It's just a matter of training and having pride in one's work. I can tell when one of these kids finally gets it. His product definitely steps up a notch, not just for my projects, but for all the work he does for the other engineers as well.