Learn some tips on how to install two-phase light pattern!

A very frequent question among electricians and those interested in electricity is how to proceed with the installation of a Power Supply Pattern, or better known as “Light Pattern”. Through this article we will take some doubts, give some tips and present the step by step of the installation of one of the most installed standards in the residential environment, the standard with an aerial connection extension to 2.3 or 4 power wires, this energy standard it is installed on a wall or wall and read by the public way, so we will increase our knowledge.

All the information in this article is in accordance with the standard ND 5.1 and ND 5.2 of the CEMIG energy concessionaire, although all concessionaires are well aligned in terms of the technical installation, for other regions of Brazil, other requirements may not be addressed in this article.

Types of electrical installations:

To start, we need to know what are the types of electrical installations offered by utilities today, the energy standards differ by the number of phases received from the network and the voltage value. This definition of the type of energy standard is made by the amount of load that will be demanded by the customer, we can find single-phase standards (127V), Biphasic Standards (220V) and Three-Phase Standards (220V).

Lifting loads:

The first step is to raise the amount of charge in the residence, this amount of charge is made through a small conversation with the customer, where he asks about the possible electrical equipment that will be used in the installation. We should ask some simple questions, such as how many showers? Will electric motors be used? If you need bombs? and etc.

It is important to consider whether the customer’s equipment is 127 Volts or 220 Volts because if the answer is 220 Volts, the single-phase 127 Volt standard will be eliminated immediately. With the information in hand, we will lift the demanded load and define what kind of standard will be needed. To perform this calculation we must take the value of the total power of the equipment and add the values, this way we find the total power, see the example below considering the power in the two phases:

Demand calculation table and residential load

In CEMIG’s ND – 5.1 we find a table with the average power of residential equipment, at this moment the table can be very useful to assist in calculations:

Table CEMIG power of residential equipment

Choosing the input pattern:

With possession of the total demand for all equipment, we can now define the type of standard for the residence, the CEMIG ND-5.1 standard addresses that for 127 volts a maximum power of 10 KW is allowed, for 220 volts a power of up to 10.1 to 15KW, for three-phase 220V power the allowed power is 15.1 to 75 KW.

Bearing in mind that this total power, our example needs a two-phase 220V standard.

How to choose between two-phase or three-phase? In order to define between the two types of installation, we must first know that for each voltage range installed, the energy concessionaire charges a fee for this supply, so it is necessary to realize the cost-benefit ratio.

If there is no demand for a two-phase pattern then do not install one, in the same way for the three-phase pattern. What happens is that in the past we used the argument that a 220V standard used less energy, this information is completely wrong, using an energy standard with phases that is not demanded is throwing money away.

To base it, perform the demand calculation in KVA, multiplying the total current by the voltage, if the value found is greater than 30.8 KVA, it will be necessary to use a three-phase standard in the installation because under these conditions the two-phase standard will not meet the demand installation.

Take the example:

Va = 55A.220V Va = 12100 KVa = 12.1

In the example above we consider the maximum power factor (= 1), we can see that the maximum power demand per phase is 12.1 KVA, so we can install a two-phase standard with a bipolar circuit breaker from 60A to 70A.

Advantages and disadvantages of a two-phase pattern:

When installing a biphasic pattern some positive and negative points must be taken into account and explained to the customer.

Strengths:

  • The circuit can be dimensioned in a balanced way;
  • Avoids overloads due to the use of simultaneous equipment;
  • Enables the use of wires with a smaller area in 220V voltage equipment;
  • It allows the use of simultaneous showers.

Negative points:

  • Value of the energy utility fee is higher;
  • Uses more wires in the installation due to the need to bring two stages of the pattern to the residence;
  • Need for 02 rods for standard grounding.

How to set up the residential two-phase standard:

The electrical power connection pattern consists of a pole, meter box, conduits, wires, grounding rod and protective circuit breaker. For the practical example we will exemplify the two-phase pattern with a meter visible on the street. (To register consumption it is not necessary to enter the property).

The materials required for installation are listed according to ND 5.1 CEMIG, we will have two possible models for this type of standard, see model 1:

List of materials according to ND.5 CEMIG – Standard model1

Now look at the list of materials to perform the installation and assembly of the two-phase model 02:

List of materials according to ND.5 CEMIG for standard installation model 2

With the possession of all material, we carried out the assembly of the infrastructure, remembering that it is necessary to carry out some interventions in the masonry and the wall to be installed must be on the boundary of the residence (it may be necessary to activate a bricklayer). The infrastructure must comply with ND 5.1

Assembly and installation of standard model 1

This is the first possible pattern model for this type of two-phase power pattern installation, see that it takes advantage of the structure of the house itself.

The height of 3500mm of the entry post must be respected or you may not have your standard approved for installation. The energy meter box must be fixed at a height of 1500 mm for easy reading.

Another point that should not be overlooked is the installation of the grounding rod, it must be carried out in an appropriate box for the inspection and connection of the grounding cable (copper cable of at least 16mm²), it is advisable according to NBR 5410 to install a grounding electrode per phase of the circuit.

Now notice the second possibility, no less used:

Assembly and installation of standard model 2

Just as the first model is necessary to respect the height of 3500mm of the input isolator, the energy meter box must also be fixed at a height of 1500 mm to facilitate reading. Not least, the installation of the grounding electrode (grounding rod), it must be carried out in an appropriate box for the inspection and connection of the grounding cable (Bare copper 16mm²).

The internal electrical installation of the two energy standard models is common for both, as installations must be carried out in accordance  with ND 5.1. First, the pipe (pole / pole) used to install the pattern must have a 13 mm diameter hole located 1.5 meters from the base, in addition it is common to find the pole with the installation of the conduit, already made, this makes it much easier installing the pattern. The next step is to take the 03 25mm² cables to the waiting point for CEMIG’s connection. The cable colors must conform to the standards, so there are two cables in black and one cable in blue.

The phases (black cables) pass through the input circuit breaker, the blue cable (Neutral) goes straight and the connection is made with the cable connected to the grounding rod and the green ground cable.

The conductors’ tips wait for the connection to be made by the concessionaire technician, remembering that it is important to install a tubular terminal whenever flexible cables are used.
The cables that go to residence must be waiting to be connected to the meter, so the structure is similar to the image below:

Standard cable layout model

The protective conductor must necessarily exist. This conductor is green or green and yellow and must be taken to the pass box or internal distribution board ( collective standards ). The conductor used for grounding must be made of copper,  without insulation , rigid, and be exposed until the last grounding rod.

The cables that come out of the meter box must reach a passage box where the connection of the property’s power cables will be made. For installation with flexible cables, it is necessary to use tubular terminals for connection to the circuit breaker and also for the energy meter:

If there are still any questions in this video, we’ll talk more about input patterns:v