With the rapid development of science and technology, the electrical level of many countries and regions is gradually improving, and the scope of application is becoming wider and wider, such as home solar power system. Especially in construction electrical engineering, the installation of electrical systems has a great impact on the progress of the project and the safety of the project.
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Therefore, how to install and debug a low voltage power distribution system is an important part of current construction electrical engineering. So what does a low voltage power distribution system consist of? What are the main equipment? What are the functions of each part? This article will introduce it to you in detail.
1. Composition of low voltage power distribution system
A low voltage power distribution system generally includes: low-voltage power distribution panels, switch cabinets, switch boards, lighting boxes, power boxes and motor control centers.
Low-voltage cabinet transformer section: transformer → incoming line cabinet → reactive power compensation cabinet → busbar cabinet → outlet cabinet
2. Main equipment of low voltage power distribution system
① Low-voltage incoming cabinet
- The main power incoming line is equipped with a main circuit breaker, and the front end is connected to a converter like w inverter or w inverter;
- The first cabinet connected from the low-voltage side output of the transformer to the initial end of the 6KV/10KV bus: it is called the incoming line cabinet, also called the variable-low incoming line cabinet;
- The incoming line cabinet is the main switch cabinet on the load side. This cabinet is responsible for the current carried by the entire busbar. The switch cabinet is connected to the main transformer and the low-voltage side load output;
- In terms of relay protection, when the busbar or circuit breaker on the low-voltage side of the main transformer fails, the over-current protection on the low-voltage side of the transformer must be used to trip the incoming line cabinet switch to remove the fault;
- Follows the functions of isolating, breaking, protecting, monitoring, and controlling the power supply quality and safety of the main circuit.
② Capacitor compensation cabinet
The function of capacitor compensation cabinet:
Unlike off grid batteries system, the grid-connected systems are greatly affected by the power quality of the grid. Capacitor compensation cabinets can improve the power factor of the low voltage power distribution system and reduce the energy waste caused by low power factor of the power grid.
Power factor:
Power factor refers to the ratio of active power to apparent power: cosφ=P/S. The size of the power factor is related to the load properties of the circuit, (such as incandescent light bulbs, resistance furnaces, etc.) The power factor of the resistive load is 1.
In circuits with inductive loads (such as motors, transformers, fluorescent lamps and electric arc furnaces, etc.), the power factor changes between 0 and 1, that is:
O.
The dangers of low power factor：
- Damage the voltage quality
- Reduce the equipment service life
- Greatly increase the line losses
- Reduce the equipment utilization
- Increase the electricity expenses and thus increase the product costs
The size of the power factor is related to the load properties of the circuit. In the AC circuit, the cosine of the phase difference (Φ) between the voltage and the current is called the power factor, represented by the symbol cosΦ. Numerically, the power factor is the ratio of active power to apparent power, that is, cosΦ=P/S
The relationship between active power, reactive power and apparent power:
Due to the existence of inductive, capacitive or non-linear loads, reactive power exists in the low voltage power distribution system, resulting in active power not equal to apparent power.
The relationship between the three is as follows:
S=P+Q
S is the apparent power, P is the active power, and Q is the reactive power. The units of the three are VA (or kVA), W (or kW), Var (or kVar).
In the above formula, if the value of KVAR is zero, KVA will be equal to KW. Then 1KVA of electricity sent by the power supply bureau is equal to the user's consumption of 1KW. At this time, the cost-effectiveness is the highest, so the power factor is very important for the power supply bureau.
If the user does not achieve the ideal power factor, it is relatively consuming the resources of the power supply bureau, so this is why the power factor is a regulatory limit. Different countries and regions have different regulations. Currently, as far as China is concerned, the power factor regulation must be between 0.9 and 1 for inductance. If it is lower than 0.9, there will be punishment.
Benefits of improving power factor to user end:
- By improving the power factor, the total current in the line and the capacity of electrical components in the low voltage power distribution system, such as transformers, electrical equipment, inverter cable, etc. are reduced, thus not only reducing investment costs, but also reducing the loss of its own electrical energy.
- Ensuring good power factor values can reduce voltage losses in the low voltage power distribution system, make the load voltage more stable, and improve the quality of electric energy.
- It can increase the margin of the system and tap the potential of power supply equipment. If the power factor of the system is low, then while the capacity of the existing equipment remains unchanged, installing a capacitor can improve the power factor and increase the load capacity.
- Reduce the user’s electricity bill: By reducing the loss of the above components and improving the power factor, the electricity bill is discounted.
Specific measures to improve power factor:
Factories typically have the following load characteristics:
-
Capacitive loads: servers (switching power supplies), rectifiers, UPS, LED lights
-
Inductive loads: water pumps, air conditioning motors, etc.
-
Resistive load: heater, incandescent lamp, etc.
How to improve power factor:
- Choose the correct model and capacity of asynchronous motor
- Select a matching transformer according to the load
- Synchronized operation of asynchronous motors
- Shunt capacitor
How parallel capacitors work
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The most common method to improve the power factor is to connect reactive power compensation capacitors in parallel to the power supply equipment.
After the capacitors are connected in parallel, the current of the capacitor will offset part of the inductor current, thereby reducing the inductor current and the total current. The phase difference of the voltage and current becomes smaller and the power factor increases.
The dangers of capacitor overcompensation
- Increase electricity charges
- Increase line loss
- Reduce load voltage
Main measures to prevent capacitor overcompensation
- When capacitive load is used, the input of capacitors should be reduced or the input of reactor should be increased. The power factor should be monitored in a timely manner and the power factor should be ensured to be within 0.8-1.0 by adjusting the operating mode and switching compensation device. Adopt automatic capacitor switching device to automatically switch in or out the capacitor bank according to changes in load.
- Also called busbar segmentation cabinet, it is a device used to connect two sections of busbar;
- Mainly used in low voltage power distribution system with two power supplies and two transformers. The main control cabinets of the two transformers are separately wired to the contact cabinet;
- On the contact cabinet, the lower port is connected to the outlet wires of the two main controllers, that is, one uses the upper port to enter the line, and the other uses the lower port to enter the line.
- For two or more simultaneous power supply systems, when another system has a power outage or power failure, the other power supply system can provide power to the outlet cabinet of this power outage system through the contact cabinet, so that this power outage system can be used. The system's power distribution group is energized.
④ Outlet cabinet
- The outlet switch cabinet of the low voltage power distribution system, with lower-level electrical equipment;
- Install an outlet switch cabinet on the low-voltage side of the transformer to send electric energy to the low-voltage bus through the incoming line cabinet, and then to low-voltage loads or electrical equipment through the switch cabinet. This switch cabinet is an outlet cabinet.
3. Lightning protection
- Generally, the first-level arrester is installed in the main power distribution, and choose SPD with relatively large flow capacity (80KA~160KA depends on the situation), such as PT and arrester cabinet in the on-site medium voltage part;
- Install a second-level lightning arrester (10KA~40KA) at the subordinate regional distribution box, such as the lightning arrester at the front of the low-voltage entry cabinet at the installation site;
- Install a third-level signal arrester at the front end of the equipment, such as a surge protection device for wall boxes and column cabinets.
Installation requirements
- Installing SPD (lightning arrester) requires a grounded flat iron nearby the installation site so that lightning waves can be quickly discharged when passing through the arrester;
- The grounding resistance needs to be less than 1 ohm, and in some areas with special regulations, it should be less than 4 ohms;
- Because voltage-limiting SPDs are generally used, the line length between them should not be less than 5m.
Power outage maintenance procedures
Power outage → discharge → power inspection → install grounding wire → hang signs → install barriers, etc.
Basic steps for power outage: low voltage first, then high voltage, load first and then isolation.
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Low Voltage System for entire home
Post
by Bunty » Sun Dec 24, 1:31 am
We are considering putting LED light strips through out the home in soffit ceilings, kitchen cabinets, outdoor patio, etc.
Wondering, if anyone has experience in building/installing the low voltage system for entire home.
Any guidance on what to look for.
Thanks
Re: Low Voltage System for entire home
Post
by lthenderson » Sun Dec 24, 9:41 am
No personal experience but a good friend of mine bought a home that was entirely low voltage. The person who built is was a former engineer and had a rack of homemade bread boards controlling various functions throughout the house. My friend loved the system but he had a knack for figuring out problems and making things work. I on the other hand, have just a basic working knowledge of 110V electrical work and looking at all those breadboards and wires going every which way made my head hurt.
Probably the biggest thing that would give me pause is that having low voltage might limit my options if I were to remodel or change out fixtures.
Re: Low Voltage System for entire home
Post
by Watty » Sun Dec 24, 10:00 am
Bunty wrote: Sun Dec 24, 1:31 am
Any guidance on what to look for.
A couple of things;
1) Consider that having an unorthodox system might hurt the resale value of your home. Adding 110v wiring later could be very expensive.
2) Be very cautions about buying systems which might not be available in 10+ years. I forget what it was but there was a post awhile back where someone was dealing with a failed specialty switch which was no longer available. Consider buying spares of switches and convectors which might not be available in the future.
3) I don't have a clue how inspections, permits, and building codes would work with this so be sure to look into that. Your insurance company may also need to know.
Re: Low Voltage System for entire home
Post
by rkhusky » Sun Dec 24, 10:08 am
I knew someone who had low voltage throughout the house for lighting. The lights still used 120, but were controlled by low voltage relays in the ceiling, so only the switches on the wall were low voltage.
Are you planning to run wiring in the walls, on the walls, or use wireless controllers? The latter would be the easiest.
Re: Low Voltage System for entire home
Post
by sfwood » Sun Dec 24, 10:49 am
If the low voltage is to exist alongside standard wiring, be aware that running both 120V and low voltage cabling in walls / ceilings / floors isn't straightforward and has specific requirements. For example, you can't just install a new low voltage cable along the path of an existing 120V cable. If DIY make sure to plan carefully or hire someone who knows what they're doing.
Re: Low Voltage System for entire home
Post
by Valuethinker » Sun Dec 24, 10:57 am
If one has LED lighting strips, does one need low voltage wiring?
Isn't it just the strips are separate circuits, connected to the usual 120v mains? i.e. local transformers for each strip?
Re: Low Voltage System for entire home
Post
by dukeblue219 » Sun Dec 24, 11:01 am
What voltage are we talking about here? 28V? 12V?
You can't realistically run 5V throughout the house because the resistive losses will be obscene. 28V makes a lot of sense but now you need to down convert to various voltages, and efficient, low noise DC to DC conversion is not trivial.
You can do this if you have an entire long-term ecosystem of devices on the same rails, but otherwise you'll have a mess of various point-of-load converters that really isn't any better than 120v AC to each load.
Re: Low Voltage System for entire home
Post
by suemarkp » Sun Dec 24, 11:44 am
I worked in labs that had 28 VDC power distribution. I believe Square D QO circuit breakers and load centers are listed for DC distribution. I would not run DC instead of AC, but run it in addition to the 120/240V wiring.
You can use regular romex and install it like it is 120V wiring. In the NEC, this would most likely be class 1 low voltage wiring. Class 2 and 3 low voltage gives you more allowances, but each circuit is limited to 100 watts and it needs to be sourced from a listed CL2 or CL3 power supply. If you have a large 12 or 24 volt DC supply feeding a dc loadcenter with 10, 15, or 20 amp breakers, you are way past the CL2/CL3 limits.
If you do this, to me using a 12/24 VDC supply that is plus or minus 12V from the "neutral" would be most analagous to 120/240 VAC wiring. But many people could be fooled so using different a different looking cable method for the DC circuits (MC cable, TC cable) may be a good idea.
Some other issues. Most switches you buy are rated AC Only. You can get AC/DC switches, but they make a loud clunk and will cost more. If you want DC power outlets, Im not so sure there is a standard yet for those.
Finally, you could run a bunch of class 2/3 circuits each from an array of separate listed CL2 power supplies, and just run listed CL2/CL3 cabling in the walls and directly to lights, but controls and switches are still somewhat crappy if intended for DC LED lighting. I think you are better off using a 120V system and using LED lights that have 120V drivers.
Mark |
Somewhere in WA State
Re: Low Voltage System for entire home
Post
by suemarkp » Sun Dec 24, 11:51 am
sfwood wrote: Sun Dec 24, 10:49 am
For example, you can't just install a new low voltage cable along the path of an existing 120V cable. If DIY make sure to plan carefully or hire someone who knows what they're doing.
Um, yes you can. As long as the house wiring is a cable method like romex, you can run it and LV cables side by side and through the same bored holes. May not always be a good idea based on the signal, e.g. unbalanced audio cables, but not code required. Separation is required in boxes where the individual conductors are stripped from their outer sheath.
Mark |
Somewhere in WA State
Re: Low Voltage System for entire home
Post
by IMD801 » Sun Dec 24, 12:05 pm
What's the upside of running a low voltage system as opposed to just using LED bulbs which draw very little power from standard 110V? Seems like it would be cheaper (and dramatically simpler) and similarly efficient to just tap in to your existing system.
Re: Low Voltage System for entire home
Post
by Point » Sun Dec 24, 12:09 pm
Why? Cost differential? Better control of devices? Coolness factor?
We run LED via 120v, and have smart lights where needed controlled by WiFi remotely (apple home). We also have solar, so our annual cost is zero for electricity (sunk cost).
We have zero negative impact long term too due to 120V standard.
Re: Low Voltage System for entire home
Post
by billaster » Sun Dec 24, 12:37 pm
IMD801 wrote: Sun Dec 24, 12:05 pm
What's the upside of running a low voltage system as opposed to just using LED bulbs which draw very little power from standard 110V? Seems like it would be cheaper (and dramatically simpler) and similarly efficient to just tap in to your existing system.
Low voltage house wiring has only become practical with the introduction of LED lighting. 120V circuits are overkill for LED lighting. There are two major advantages to low voltage lighting.
The first is that you can typically use smaller wiring which saves on copper because LED lighting requires less power. The second is that you don't need to have a AC to DC converter in every light bulb. The AC to DC converter in every light bulb takes up space, which limits their use to larger bulb sizes and they are components susceptible to failure from heat generated by the LEDs in the bulb. It also increases the cost of every bulb. It is much more efficient and reliable to have one central large AC to DC converter that is independent of the lighting heat sources than to have dozens of little AC to DC converters scattered around the house in each LED bulb or fixture.
Re: Low Voltage System for entire home
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by GAAP » Sun Dec 24, 1:58 pm
Are you thinking of putting a low voltage electrical distribution in the house, or just using the typical strip lights with ballasts? The second is likely to be much easier in most homes. If you go that way, you can save some power by using ballasts that meet California Title 24 efficiency requirements.
The requirements you listed are fairly typical, and fairly easy to install (depending upon power availability). Be sure to choose the right color temperature for each use, and use wet-environment equipment outdoors. Higher CRI values will probably also be appreciated if you don't want that industrial look. You may also have some locations where a ballast with multiple outputs is useful or necessary. In general, determine all of your needs first, then evaluate options based upon ability to meet those needs.
“Adapt what is useful, reject what is useless, and add what is specifically your own.” ― Bruce Lee
Re: Low Voltage System for entire home
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by ncbill » Sun Dec 24, 2:09 pm
Stick with 120VAC here in the USA.
Even low-power DC (under 50V) requires more expensive breakers, switches, etc. versus standard 120VAC components.
Re: Low Voltage System for entire home
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by snackdog » Sun Dec 24, 2:38 pm
If you are looking for more details, kindly visit low voltage distribution cabinet.
24v systems were fairly common in custom and high-end homes in the 60s and 70s. I have seen many and our current home has the system. One advantage is that a bundle of 24 gauge wire can be cheaply run to the location of every switch box enabling it to control every overhead and wall socket in a large area. The 120v romex only needed to run to the lights/outlets, not the wall switches. Low voltage systems also allow as many switches as desired, not just one or two, per light/outlet. Switches can be illuminated with 24v for added glamour and an indicator that the switch is on. Some houses had master panels where all the lights/outlets could be monitored and turned off or on from one location. Wiring a new switch is easy as 24v doesn't even require you to interrupt it for wiring. Most homes have a single 120>24v stepdown transformer. Each light/outlet circuit uses a relay switch in the wall or ceiling which activates the 120v power. Parts are still readily available here: https://www.kyleswitchplates.com/low-vo ... es-plates/
As for 24v or 12v LED in current homes, if you find yourself in need of too many transformers then a master transformer is fine as long as you can easily wire all the lights to it.
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