GEM Residential FAQ

GEM Residential FAQ

General (8)

How many panel circuits can I monitor with a single GEM?

Although the GEM is a 32-channel device, more than 32 branch circuits may be monitored. Two branch circuits can be monitored on a single channel. The consumption of each branch circuit combined on a channel will be totalled as one load. Combining circuits onto a single channel can be used to conserve channels.

Some typical examples would be to group the kitchen counter receptacles together, bedroom circuits together, etc. You can also group seasonal loads together such as “Heating” and “Air Conditioning”, since only one of the two loads would be operational at a time.

If I have multiple appliances on a single branch circuit, will the GEM be able to show the consumption of each appliance?

No. The channel will display the sum of all loads. Many times it is easy to distinguish which of the combined load is running. This can also be used strategically such as having a furnace and A/C unit on the same channel. Since the furnace blower is part of the A/C system, the combined loads would represent the total “cooling system” in the summer and electrical portion of “heating” in the winter

Does the GEM Measure True power?

Yes. The GEM over-samples the line voltage and load current to generate a “true” power measurement. True (or real) power is what the Electric Company charges for.

How accurate is the GEM?

Power/Energy Measurements: Typically +/- 1% plus CT accuracy
Voltage Measurement: Better than 1% with PT-Type value trimmed to a reference

Can the GEM send text or email alerts?

Alerts are the responsibility of the data host. Depending on the data host used with the GEM, alerts may be available.

How much power does the GEM consume?

The GEM typically consumes less than 1 watt.

Does the GEM hold all historical data and perform graphing?

No. It is important to understand that the GEM requires a “Data Host” to store realtime data from the GEM. The “Data Host” will provide an interface allowing “Live” and “Historical” data to be viewed and charted for analysis. Refer to the “Data Host” section for more information.

Can the GEM do “net” metering?

Yes. If you have a grid-tied inverter from a renewable energy source such as solar or wind, the GEM can be connected to monitor the main panel and inverter (plus other loads).

The resulting data obtained will be:
• “Net” power (energy bought – energy sold)
• Energy sold
• Energy purchased
• Energy generated
• Energy consumed by home loads.

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Installation (7)

Where should the GEM be mounted?

The GEM is typically mounted next to or close to the electrical panel within range of network access and the CT leads.

Can I install the GEM inside my electric panel?

NO! This is absolutely forbidden. Since all connections to the GEM are isolated from live powerline voltages, it is important to keep these away from potential high voltages. A separate electrical style box may be installed next to the panel ensuring that no line voltages (120V or 240V) enter this enclosure.

What is a Current Transformer (CT)?

The current transformer (CT) is a non-intrusive device used to measure the electrical current from a load. The 3 most important current transformer criteria are:

  • Safety certified by organizations such as UL, CSA, ETL, NRTL, etc. (Most of our CTs are UL recognized for USA and Canada)
  • Accurate (Most of our CT models fall within +/-1% accuracy)
  • Proper style for the application.There are two general styles of current transformers:
    • Closed CT
    • Split-Core CT

Do I need an electrician to install the CTs?

The GEM CTs must be installed by a qualified electrician. Once the CT leads have exited the panel and are properly anchored or secured, the remaining external wiring may be done by the homeowner. The CT signal is low-voltage and galvanic isolated from the power line. This makes it simple and safe for the homeowner to connect.

Can I extend the CT leads?

Yes, but it is not recommended. Extending CTs can lead to accuracy loss due to noise or signal loss. The GEM was designed to be mounted next to or very near the electrical panel.

What is a Potential Transformer (PT)?

The PT is used to sample voltage in order to calculate True Power.

Our residential GEM uses a wall adapter as a PT but other options are available to hook directly to a breaker.

Can the PT be connected to 240V?

You can connect a “special” PT to 240V, contact us for more information.

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Current Transformer (CT) Selection (6)

Do I need one or two CTs for a 240V breaker?

If the 240V breaker has a neutral, you must have a CT on each leg of the breaker. If there’s no neutral then it’s balanced, one CT can be attached to one leg of the 240V breaker and the value can be doubled via settings

Should I get “Donut” or “Split” style of CTs?

Donut-style CTs require more effort to install but are less obtrusive and cheaper then Split-style CTs. The wire has to be removed from the breaker and the CT has to be slid over.

Split-style CTs are larger than and more expensive than the Donut-style CTs but don’t require the breaker wire to be removed. They’re commonly used on Main breakers as the wires can’t be disconnected from the main breaker.

For more information on the different installations of each CT style, click this link.

Can I use CTs from other sources?

We don’t recommend using CTs from other sources.

You can only use the CTs if they are safety certified for the country they’re used in. They must output 0.333mV. It’s the responsibility of the customer to calibrate their GEM CT settings for 3rd party CTs using a known load such as an 80W light bulb. Any damage caused from using a third party CT voids the warranty of the GEM.

What is a Current Transformer (CT)?

The current transformer (CT) is a non-intrusive device used to measure the electrical current from a load. The 3 most important current transformer criteria are:

  • Safety certified by organizations such as UL, CSA, ETL, NRTL, etc. (Most of our CTs are UL recognized for USA and Canada)
  • Accurate (Most of our CT models fall within +/-1% accuracy)
  • Proper style for the application.There are two general styles of current transformers:
    • Closed CT
    • Split-Core CT

Do I need an electrician to install the CTs?

The GEM CTs must be installed by a qualified electrician. Once the CT leads have exited the panel and are properly anchored or secured, the remaining external wiring may be done by the homeowner. The CT signal is low-voltage and galvanic isolated from the power line. This makes it simple and safe for the homeowner to connect.

Can I extend the CT leads?

Yes, but it is not recommended. Extending CTs can lead to accuracy loss due to noise or signal loss. The GEM was designed to be mounted next to or very near the electrical panel.

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Temperature Measurements (3)

What type of temperature sensors will the GEM accept?

The GEM supports DS18B20 temperature sensors.

If I use two temperature sensors, does that mean I can only monitor 30 channels instead of 32?

You can still monitor with the 32 channels. The temperature channels are independent from the energy monitor channels.

Can I use more than eight temperature sensors?

No. The GEM supports a maximum of eight temperature sensors.

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Pulse Counting Inputs (3)

What are the pulse counting channels used for?

The pulse counting channels can be used to monitor anything with a pulse output, some examples are:

• Water consumption
• Natural gas consumption
• Electric meter
• Traffic/occupancy

What if my water or gas meter has no pulse output?

For gas, your existing gas meter has to be replaced with a meter with pulse output.

For water, a water flow sensor or water meter with pulse output can be installed after your existing water meter.

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