sentence clarification

Hi,
Here are two sentences I can't understand. (esp. the underlined part).
1- "Equipment may be placed in a cabinet if the stealth support structure is incidental to a non residential use."
2- "Towers erected and maintained for a period not to exceed 45 days for the purpose of replacing an existing tower, testing an existing or proposed network, or special events requiring mobile towers."

Any clarifications in meaning is appreciated in advance,

Regards,

Iman