Frequently Asked Questions

The information below offers descriptions, explanations, and answers to a variety of frequently asked questions. If you have a question not answered here, contact us, and we'll be happy to help you. Click a link below to jump to the section or topic you're interested in.
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What are the differences between PV wire and USE-2 wire?

Whereas USE-2 wire has long been accepted for PV module interconnections, PV wire is newly addressed in the 2008 edition of the NEC. Though their construction and performance requirements are similar, some variations between PV wire and USE-2 wire do exist due to their unique installation conditions. Below is a comparison of these two types of wires based on their usage, construction, and testing requirements:


A PV wire, a with 90ºC wet rating and up to 150ºC dry rating, is dedicated to interconnecting PV modules. A USE-2 wire is designated as an underground service entrance cable typically for connecting to the terminals of service equipment. It is limited to installations in a maximum of 90ºC wet and dry conditions.

Both USE-2 wire and PV wire can be rated 600 V. However, a PV wire can also be rated 1000 V and 2000 V to accommodate photovoltaic modules intended for use in systems with a system voltage greater than 600 V. Per the NEC, a USE-2 wire is suitable for use in grounded PV arrays only, but a PV wire can be used within both grounded and ungrounded PV arrays.


A PV wire comes with a thicker insulation or jacket to provide additional mechanical protection against the physical abuse that USE-2 wire typically receives. PV wire employs stranded copper conductors to make it flexible enough for the intended application. On the contrary, a USE-2 wire can employ either solid or stranded conductors made of copper, copper-clad aluminum. or aluminum since it is typically installed in locations not subject to movement or mechanical damage. The minimum conductor size for a USE-2 wire is 14 AWG, but a PV wire can employ a smaller conductor size down to 18 AWG.

Insulation and jacket materials, both PV wire and USE-2 wire use thermoset insulation and jacket typically made of XLPE or EPCV. Nevertheless, other thermoset materials such as CP over EP, CP over EPCV, SBR/IIR/NR, and EP are also available. A PV wire may also be constructed similarly to Type UF but uses an additional 15 mils of 90ºC wet and dry rated integral PVC insulation and jacket.

Testing Requirements

Because a USE-2 wire is typically installed underground or in similar locations where a flame may not propagate, but a PV wire can be exposed in an installation, a flame test is required only for PV wire. On the other hand, overload tests and mechanical abuse tests, including crushing resistance and impact resistance, are applicable only to a USE-2 wire.

As for sunlight resistance and flexibility at low-temperature tests, a PV wire must comply with more stringent requirements. It undergoes a 720-hour Weather-Ometer and -40ºC cold chamber conditioning. The requirements for a USE-2 wire are a 300-hour Weather-Ometer and -25ºC cold chamber conditioning.

In summary, when compared to a USE-2 wire, a PV wire has superior sunlight resistance and low-temperature flexibility in addition to a thicker insulation or jacket and a proven level of flame resistance. Given that a PV wire can facilitate the use of ungrounded PV arrays as well as transformerless inverters, it is anticipated to grow in popularity for module interconnections.

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What is a PV adapter and what type do I need?

PV adapters allow a user to connect a module to an inverter equipped with a different type of end connector system. This allows the user to connect different brands of solar modules to another manufacturer’s equipment, for example, an inverter.

It is essential that adapters not only have the physical format to attach the module to the inverter, but they must have the appropriate polarity.

An adapter plugs into the module's original cable and then provides the connection appropriate for the polarity of the original cable. They will usually have a positive (+) or connector on one end and a negative (-) on the other.

An important consideration is the terminology used to describe the physical connector at each end of the adapter.

In most electrical industries, connectors are described as Male and Female, but this applies to the metal contacts themselves, not the plastic insulator that houses them. For some manufacturers of solar equipment, such as Amphenol, Tyco SolarLok, Multi-Contact, and Radox connector systems, the housing of the connector pins appear opposite from standard electrical industries.

To Illustrate:

The male pin has a housing with a relatively large opening in the end, and the pin itself is recessed within.

The female pin has a housing that has a long, narrow tip that fits into the male housing when they are mated.

This appearance is just the opposite of what the terms Male and Female usually bring to mind and is the biggest source of problems in ordering exactly what you, the customer, needs.

When ordering adapters for your PV-Cables, it is vital to specify the physical type of connector for each end as well as its polarity.

Enphase Energy Application Note - Mating Microinverters With PV Modules for Correct Polarity:

The following helpful brief was prepared as an application note by Enphase Energy in October 2010 to provide clear guidance for mating microinverters with various DC connector types with PV modules (or adapter cables) and to ensure correct polarity between the microinverter and the PV module:


Microinverters are manufactured with two types of DC connectors for mating with PV modules. For example, microinverters ship with the following connector types:

1. MC-4 compatible locking connectors (part number suffix S12)
2. Tyco style locking connectors (part number suffix S13)

The polarity of the DC connectors on the microinverter varies with the type of connector.

When your microinverters are built with MC-4 compatible (S12) connectors:

Positive DC output of the PV module (+) connects to the microinverter connector labeled negative (-).

When your microinverters are built with Tyco (S13) connectors:

Positive DC output of the PV module (+) connects to the microinverter connector labeled positive (+)


As we see above, connector labels do not always map to the corresponding positive or negative input of the microinverter.

PV module connector labels may not map to the corresponding output of the PV module either.

Microinverters should be ordered with the correct connectors for your PV modules.

But if the retermination of your module’s connectors is required, it is critical that the positive output of the module be identified from labeling on the PV junction box. Connector labels can be misleading.

It is critical to follow these guidelines to avoid reversing the polarity between your PV module and the microinverter.


Mating a microinverter with MC-4 connectors to a PV module with MC-3 connectors using an adaptor cable:


Tyco Mating:



The MC4 connector format is a design originated by and belonging to Multi-Contact, and is not a standard configuration such as a NEMA type connector would be. Multi-Contact does not release to their completion any of the vital information concerning our product, especially the materials used, mechanical/dimensional data, or product characteristic controls used to maintain product quality and proper function. So any company that makes an MC4 compatible connector is quite simply guessing what all of these characteristics are. The seemingly simple and unimportant PV module connector has some very rigorous and extreme demands on it: survive outside in temperatures swinging from below freezing to near boiling, in direct sun or driven snow, arid dry or soaking wet, for 20+ years. This is while conducting and protecting upwards of 20-30kW DC of energy without failing. All facets of a connector product degrade over time, especially in these conditions, so the key is to have it always stay in a safe region for its expected life. The smallest inconsistencies or defects, can over a long period of time, easily push certain key properties out of the safe region and into a run-away failure. Such inconsistencies may at first be largely unnoticeable from a macro level: connectors mate together, keep water out and pass current without showing any noticeable signs of excessive contact resistance/heat. But over time (could be on the scale of months or years), the effects of these issues or mismatches can feed into exponential growth in resistive heat, seal integrity loss, or material reactions. All of which can easily become a shock or fire hazard. If you consider how unlikely (and by that we mean impossible) it is for someone to guess right all the dimensional schemes, tolerances, materials and control features of such a product, you can see how such inconsistencies can easily find their way into a compatible product.


None of the major 3rd party testing agencies (TUV, UL, CSA, ETL) will allow for the certification of PV connectors from different manufacturers without the written consent of all companies involved and the proven comingling and sharing of vital design and material information. Such a situation, at least from what we have been able to find, does not exist between any of the popular PV connector manufacturers. Certainly, no such agreement exists between Multi-Contact and another company. This is explicitly mentioned in the standards that are used to certify PV connectors.

For example:

UL6703 (Connectors for use in photovoltaic systems), section 1.5: This standard covers PV connectors whose dimensions are not defined in any national or international technical standards. Connectors are identified and tested with compatible mating part (or parts if multiple exist) and are to be of the same brand, unless multiple product manufacturers are submitting under the same evaluation for the purpose of proving intermatability.

So even though a module manufacturer may have a module certified with connector company s product and the same product also certified with connector company Bs product on it, this does not mean that the interconnecting of the 2 different modules is also certified. Since the NEC code as well explicitly states that a PV connector used in a PV system must be of a latching or locking type and be listed (certified) for the intended use, then mixing the mentioned pair of modules in a PV system as well is considered not to code.

National Electric Code (NEC)

The NEC specifically states the following:
690.4 General Requirements.
(B) Equipment. Inverters, motor generators, PV modules, PV panels, ac PV modules, dc combiners, dc-to-dc converters, and charge controllers intended for use in PV power systems shall be listed for the PV application.

Since PV connectors are not certified by any agency for cross-mating with another companyÂÂÂ’s product, doing so in a PV installation is using it in a way that is not listed by the certification agency that evaluated the module product and thereby is violating the NEC code in doing so.

Warranty and Liability

With all of the above in mind, I think it is easy to see why Multi-Contact does not and cannot warranty the connecting of our PV connectors to those from other companies (and the same statement/situation is true from most other competitors’ point of view). We consider this a very serious issue and have seen in several real-world situations that cross-mating does cause problems and has resulted in fires and electric shock.

How do I determine what is a male or female connector?

The pictures below illustrate the differences. Roll your mouse over a thumbnail for a closer view.

Huber+Suhner Radox





Multi-Contact MC3 (Solarline 1)





Tyco Solarlok

Male (Neutral)


Female (Positive)


Tyco Branch


Female (Negative)


Amphenol Helios H4





Multi-Contact MC4 Branch Connectors

These waterproof Y-connectors make it possible to parallel wire PV modules with Multi-Contact output cables. The max current allowed through connectors is 30 amps.

1 Male, 2 Female


1 Female, 2 Male


Multi-Contact MC4 Locking Sleeve

Use the MC4 Locking Sleeve when solar modules are equipped with Multi-Contact MC4 connectors. In order to comply with the 2008 National Electric code for accessible arrays, the plug connection must be secured with the UL-approved, pluggable safety lock clip (PV-SSH4). Once the clip is installed, the PV plug connection can only be unlocked using the PV-MS tool.


Hosiden MC4





SMK Connectors





Easy snap-lock mating system for quick field or factory assembly.

IP67 class sealing protection against dust and water.

UL and TUV (DIN-EN) approved.

Meets NEC2008 standard for the safe installation of electrical wiring and equipment.

Long-term UV and ozone resistance

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