Three-Phase Power Installation for New Hampshire Businesses

What Bringing Three-Phase Into a Building Actually Involves

Two separate projects that have to be sequenced together, and confusing them is where most of the frustration on these jobs comes from. One is the utility bringing three-phase to the building. The other is everything from the point of supply inward, which is the part we do.

The utility side is a transformer, a lateral or a drop, and a metering arrangement. What that costs and how long it takes is decided almost entirely by whether three-phase distribution already runs past the property. Our guide to three-phase power covers how to find that out before committing to anything, and it is worth reading first, because the answer changes the shape of the whole project.

The building side is a new service entrance, new service conductors sized for the load rather than for what is there now, a meter arrangement the utility will accept, and a switchboard or panelboard to land it in. On most buildings it also means a main disconnect, grounding and bonding brought up to current requirements, and a decision about what happens to the existing single-phase distribution, which usually stays and gets fed from the new gear rather than being torn out.

Then there is the equipment itself. Three-phase at the wall is not the point; three-phase at the machine is. Feeders, disconnects and the connections to each piece of equipment are a real part of the scope and are frequently underestimated in quotes that concentrate on the service.

The Utility Application, and Who Files It

We file it, and it is worth saying plainly because it is the single most common thing businesses do not realize is included. A new or upgraded three-phase service needs an application to the serving utility with a load calculation behind it, and that application is what starts the clock on everything else.

New Hampshire is served by four utilities and they do not work identically. What each one wants, how they meter three-phase at different sizes, who owns which part of the installation and how far in advance they will schedule are all local knowledge rather than a published national standard. Getting the application right the first time is most of what separates a project that runs to schedule from one that does not.

The load calculation matters more here than on a single-phase job. Ask for too little and the service is undersized the day a second machine arrives. Ask for too much and the utility may size a transformer the business pays to have sitting there. The calculation should be built from the actual equipment schedule, including what is planned rather than only what is on the floor today.

Timelines are the thing to establish early, because the long pole is rarely the electrician. Where the utility has to extend distribution or set a new transformer, that can run to months rather than weeks, and it is set by their program and not by ours. A business with equipment already ordered and no application filed is the most common way these projects end up late, and it is entirely avoidable.

Choosing the Voltage Before the Equipment Arrives

Three-phase is not one thing, and the choice made at the service decides what equipment the building can take for the next twenty years.

Most small commercial buildings in this region land on 208Y/120, which gives three-phase at 208 volts for equipment and ordinary 120 volt circuits for everything else off the same service. It suits shops, restaurants, offices and light industrial units, and it means one service rather than a separate arrangement for small power.

Larger buildings, and anything with substantial motor load, are often better on 480Y/277, with transformers stepping down to 208Y/120 where ordinary outlets are needed. It carries more power on smaller conductors, which matters when the runs are long or the load is heavy, and 277 volt lighting is standard in buildings of that size. The trade is added transformers and a distribution system with two voltages in it.

The mistake worth avoiding is deciding this from the first machine rather than from the building. Equipment is frequently available in more than one voltage, and it is far cheaper to specify a machine to suit the service than to rebuild the service to suit a machine. Where a business is fitting out, the fit-up is the moment to settle it, and the service and switchgear work follows from that decision rather than the other way round.

The Changeover, and Working Around Trading Hours

A service changeover means the building loses power, and how long for is a planning question rather than a technical one.

Most of the work happens before the shutdown. The new service entrance, the new switchboard, the feeders and as much of the downstream distribution as can be built live are all in place before anything is turned off. The shutdown itself is the cut-over: the utility disconnects, the new service is landed and energized, and the existing distribution is transferred onto it.

Done that way the outage is usually measured in hours rather than days, and it can be scheduled for whenever the building is not trading. We have done this at night and at weekends more often than during the working day, because for most businesses the cost of being closed is larger than any premium on the labor.

What cannot be compressed is the utility’s own window. They set when they will come, and on a changeover that involves their equipment that date anchors everything else. It is another argument for filing the application early. A planned maintenance arrangement is worth considering at the same time, because a building that has just had new gear installed is the easiest one to keep records on from the start.

Where a business genuinely cannot close at all, there are ways to stage it, including temporary supplies and transferring loads in groups across more than one visit. It costs more and it takes longer, and it is worth it in a building where the alternative is losing a day of production. Around the clock cover runs through the changeover either way.

When a Phase Converter Is the Honest Answer

Sometimes the utility answer is that three-phase is not coming to the building without a bill the business cannot justify, and that is a real outcome rather than a failure. On a rural commercial property, or at the edge of a town where distribution stops short, extending it can be the largest single line in the project.

A rotary phase converter generates three-phase from the single-phase supply the building already has. It runs motors, and for a shop with one or two machines it is frequently the sensible answer: no utility project, no waiting, and a fraction of the cost. A static converter is cheaper again but derates the motor and suits intermittent use rather than continuous production.

What a converter does not do is make the building a three-phase building. The generated leg is not as stable as a utility supply, which matters for electronics, variable frequency drives and anything with sensitive controls. It has running losses. It does not help with lighting or general power. And it is sized for the connected load, so the second machine is a new conversation rather than a spare breaker.

The decision is usually clearer than it looks once the numbers are on the table: how many motors, how continuously they run, what the utility quoted, and whether the business expects to add equipment. We will say which one we would install, and where a converter is the right call we will say that too rather than selling a service upgrade that is not needed.