Okay, let's break down the electrical code requirements for electric baseboard heaters in Massachusetts, focusing on your specific setup and addressing the potential need for dedicated circuits.

Understanding the Code Landscape (Especially in Massachusetts) NEC as the Foundation

The National Electrical Code (NEC) is the starting point. Most states, including Massachusetts, adopt a version of the NEC. Massachusetts often amends the NEC with its own specific regulations. These amendments can be stricter.

Massachusetts Amendments

The Massachusetts Electrical Code is based on the NEC but often has additional requirements. You need to consult the latest adopted version of the Massachusetts Electrical Code. This is typically found in the 527 CMR.

Your Specific Scenario Heater Specs

Two 6ft, 240V, 1500W heaters Two 240V, 1000W heaters

Key Question

Can you put multiple heaters on a single circuit? The answer is yes, but it depends on load calculations and code restrictions.

Step-by-Step Analysis and NEC/Massachusetts Considerations1. Load Calculation (Critical!) Total Wattage

(2 x 1500W) + (2 x 1000W) = 3000W + 2000W = 5000W

Amperage

Amps = Watts / Volts. So, 5000W / 240V = 20.83 Amps

Continuous Load

Electric heating is considered a "continuous load." NEC requires that you size the circuit to handle 125% of the continuous load. 1.25 x 20.83 Amps = 26.04 Amps2.

Circuit Breaker and Wire Sizing Minimum Breaker Size

You must have a breaker rated for at least 26.04 Amps to handle the continuous load. The next standard size up is a 30 Amp breaker.

Wire Size

You must use wire rated for at least 30 Amps. Typically, this would be 10 AWG copper wire (check the ampacity in NEC Table 310.16, considering the wire insulation type and ambient temperature).

Derating

If wires are bundled together (as is often the case in a panel), you might need to derate the wire ampacity. Derating reduces the allowable ampacity of the wire, potentially requiring a larger gauge wire. This is based on the number of current-carrying conductors in a raceway or cable.3.

NEC and Massachusetts Rules NEC 210.23 Permissible Loads

This section dictates how much load you can put on a branch circuit. A 30-amp circuit can supply fixed lighting units and appliances.

NEC 424: Fixed Electric Space-Heating Equipment This is the most important section! 424.3(A): Branch Circuit Requirements Says that branch circuits for fixed electric space heating equipment shall be sufficient to carry the load computed in accordance with Part II of this article and shall be of sufficient size to carry not less than 100% of the total calculated load of the heaters and supplementary equipment. 424.22 Overcurrent Protection

States that overcurrent protection shall be provided as specified in 240.4. You cannot exceed the ampacity of the wire.

Massachusetts Amendments (CRITICAL)

You must look for any amendments to Article 424 in the Massachusetts Electrical Code (527 CMR). These amendments can be more restrictive. This is where you'll find the answer to whether you need dedicated circuits in your situation.4.

Dedicated Circuit Considerations (Likely for Massachusetts) Load Diversity

The fact that you're dealing with electric heating means load diversity is not generally applicable. You have to assume all heaters could be running at the same time (continuous load).

Local Amendments

Massachusetts may have a rule that requires each individual heater (or each type of heater - e.g., all 1500W on one circuit, all 1000W on another) to be on its own dedicated circuit. This is common in some jurisdictions.5.

Best Practice and Recommendation Dedicated Circuits are Safer and Easier

Even if the code allows you to combine the heaters on one circuit (which is unlikely given the total load and Massachusetts' potentially stricter rules), using dedicated circuits is generally a better practice. It simplifies troubleshooting, reduces the risk of overloading, and provides more flexibility in controlling individual heating zones.

How to Find Massachusetts Amendments1. Official Source

Go to the official website for Massachusetts regulations. Search for "Massachusetts Electrical Code" or "527 CMR". Look for the most recent adopted version (e.g., "2023 Massachusetts Electrical Code" based on the 2023 NEC, with Massachusetts amendments).2.

Look for Amendments to Article 424

Once you have the document, navigate to Article 424 (Fixed Electric Space-Heating Equipment). Carefully read any amendments that Massachusetts has made to this article. Pay close attention to anything that specifies dedicated circuits.
Example of a Possible (Hypothetical) Massachusetts Amendment

"424. Massachusetts Amendment: Each electric baseboard heater shall be supplied by an individual branch circuit. The overcurrent protection device shall not exceed the ampacity of the heater nameplate." (This is just an example - you must confirm the actual rule).

In summary, here's what you need to do


Find the Current Massachusetts Electrical Code (527 CMR).2. Read Article 424 and any Massachusetts Amendments to it. This is the most important step to determine if dedicated circuits are required.3. If the code allows it, perform a thorough load calculation as described above.4. Size your breakers and wiring appropriately.5. When in Doubt, Use Dedicated Circuits

They are safer and provide better performance.6.

Consult with a Licensed Electrician in Massachusetts

This is always the best course of action. A local electrician will be familiar with the most current code requirements and can ensure your installation is safe and compliant.7.

Permitting and Inspection

You will almost certainly need an electrical permit for this work, and it will be inspected. Make sure to get the permit before* starting the work.

Based on your description, it is highly likely that Massachusetts regulations will require at least two circuits, if not four dedicated circuits. Find and read the Massachusetts amendments to Article 424 to be certain. Flag for review