Building Lighting as Drawn vs. as Installed
Building Lighting as Drawn vs. as Installed
(OP)
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?
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?






RE: Building Lighting as Drawn vs. as Installed
RE: Building Lighting as Drawn vs. as Installed
RE: Building Lighting as Drawn vs. as Installed
RE: Building Lighting as Drawn vs. as Installed
Anyway, I now specify lighting control panels and the associated low voltage controls whenever possible.
RE: Building Lighting as Drawn vs. as Installed
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
RE: Building Lighting as Drawn vs. as Installed
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 :).
RE: Building Lighting as Drawn vs. as Installed
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.
RE: Building Lighting as Drawn vs. as Installed
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).
RE: Building Lighting as Drawn vs. as Installed
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.
RE: Building Lighting as Drawn vs. as Installed
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.
RE: Building Lighting as Drawn vs. as Installed
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.